THE  MAKING  OF 

A  MECHANICAL 

OPTICIAN 


:!iiiiliill!l!lli!liiililll!l 


THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

LOS  ANGELES 


I 


THE  MAKING  OF 

A  MECHANICAL 

OPTICIAN 


A  TREATISE  ON  THE  EQUIPMENT 
AND  MECHANICAL  WORK  OF 
OPTOMETRISTS   AND   OPTICIANS 


By  W.  W.  SLADE 

OF  THE  GLOBE  OPTICAL  CO..  BOSTON,  MASS. 


OVER  TWO  HUNDRED  ILLUSTRATIONS 


PUBLISHED  BY 

THE  KEYSTONE  PUBLISHING  COMPANY 
PHILADELPHIA,  U.S.A. 


I 


COPYRIGHT,    191 1,   BY 
THE  KEYSTONE  PUBLISHING  CO. 


VJ\P 

CONTENTS 


CHAPTER  I 

Selecting,  Installing  and  Operating  the  Machinery ' 

CHAPTER  n 

II 

Care  of  Machinery 

CHAPTER  HI 

,  , .      .  i8 

Lenses— Marking  and  Cuttnig 

CHAPTER  IV 

26 

Marking  Prisms 

CHAPTER  V 

...  38 
Marking  Prisms— Contniued 

CHAPTER  VI 

■   S3 
Cutting  Complicated  Lenses 

CHAPTER  VII 

62 

Lens  Grinding 

CHAPTER  VIII 

Drilling 

CHAPTER  IX 

87 

Mountnig 

CHAPTER  X 

„.,      ,  103 

Bifocals   

CHAPTER  XI 
Bridge  Bending  and  Truing '--^ 

CHAPTER  XII 

131 
Surface  Grinding 

CHAPTER  XIII 
Surface  Grinding— Continued '-*° 

CHAPTER  XIV 
Surface  Grinding— Continued '■* 

CHAPTER  XV 
Soldering  and  Repairing 

CHAPTER  XVI 
Soldering  and  Repairing— Continued 


154 
161 


CHAPTER  XVII 
Soldering  and  Repairing— Continued '  ^ 


THE  MAKING  OF  A  MECHANICAL  OPTICIAN 


CHAPTER   I 


SELECTING,    INSTALLING    AND    OPERATING    THE    MACHINERY 

In    beginning   this   treatise   we   have   in   mind   partially   the 
optician  who  is  considering  the  advisability  of  installing  a  plant 
to  do  his  own  work,  and,  naturally,  the  first  question  to  decide  is 
whether  it  is  advisable  to  install  such  a  plant.    The  arguments  in 
favor  of  doing  so  are  the  following :   The  accommodation  to  your 
customer,  the  new  customers  it  will  bring  by  advertising  that  you 
do  your  own  work  and  the  extra  profit.    The  arguments  against  it 
are :  The  extra  responsibility  and  labor  it  will  put  upon  you  ;  have 
you  enough  prescription  work  to  make  it  an  object,  and  if  so,  can      ,  '/■  '• 
you  aft'ord  to  hire  a  man,  and  would  it  not  be  advisable  to  use  the      i^-iXT 
time  that  you  would  put  into  this  work  to  develop  your  refracting      -,   ■,     \ 
business? 

This  matter  you  can  best  decide  for  yourself,  but,  assuming 
that  you  decide  to  take  the  step,  the  next  thing  is  to  lay  the  plans 
for  your  shop  and  select  the  machinery. 

It  was  formerly  the  custom  to  engage  an  attic  room  in  some 
old  building  on  a  side  street,  order  a  grindstone  and.  engage  car-  ,^ 
penters  and  machinists  to  fit  it  up.  As  it  was  impossible  to  esti- 
mate the  expense,  it  frequently  was  exorbitant.  Now  that  has  all 
changed,  as  it  is  possible  to  purchase  an  entire  outfit,  ready  to  run, 
at  a  nominal  cost.  This  not  only  saves  a  great  deal  of  worry,  but 
you  can  figure  the  cost  almost  to  a  cent. 

Another  great  advantage  is  that  the  outfit,  sold  by  the  whole- 
salers to-day,  can  be  used  in  any  office,  even  with  a  rug  on  the 
floor,  and  can  be  kept  as  clean  as  a  piece  of  furniture. 

The  best  place  for  a  bench  depends  somewhat  on  the  circum- 
stances. Some  prefer  to  have  an  extra  room  for  this  work  ;  others 
fit  up  part  of  the  refracting  room  or  the  reception  room.  If  you 
have  an  office,  consisting  of  only  one  room,  you  can  perhaps  select 
a  corner  near  a  window,  and,  if  you  prefer,  you  can  stand  a  screen 
in  front  of  it.  If  you  have  a  store,  it  will  be  a  good  idea  to  place 
the  bench  in  a  prominent  position,  even  in  the  window,  if  possible,     ■ 


2  The  Making  of  a  Mechanical  Optician 

thus  enabling  you  to  take  advantage  of  the  advertising  possibili- 
ties. This  question  of  space  and  location,  however,  is  not  of  very 
much  importance,  as  there  are  benches  on  the  market  that  require 
very  little  room. 

Having  well  considered  these  facts,  we  now  proceed  to  select  ~ 
the  outfit.  This  is  a  matter  which  should  be  given  considerable 
attention.  It  certainly  is  false  economy  to  buy  cheap  machinery, 
as  it  not  only  gives  trouble,  but  wears  out  sooner  and  has  to  be 
replaced  in  a  few  years.  With  the  best,  a  great  deal  of  work  is 
done  automatically,  requiring  less  time  and  attention,  and  one  does 
not  need  to  be  an  expert  to  do  good  work.  If  you  are  not  limited 
as  to  space,  we  would  suggest  a  bench  4  ft.  long  by  32  in.  wide. 
This  will  give  you  sufficient  room  to  lay  out  your  work,  so  that  you 
can  handle  it  easily. 

After  deciding  on  the  bench,  the  next  thing  is  to  select  the 
frameless  machine.  The  four  most  prominent  on  the  market  are 
the  Acme,  Gem,  Monarch  and  Simplex.  The  Acme  is  a  large 
machine,  with  a  stone  24  in.  in  diameter  and  lyi  in.  face.  It  is 
designed  to  do  heavy  work  and  can  be  used  for  both  prescription 
and  stock  grinding.  By  this  we  mean  grinding  up  quantities  of 
interchangeable  sphericals  and  cylinders.  The  Gem  is  a  medium- 
sized  machine,  designed  more  especially  for  prescription  work, 
but  stock  can  be  ground  on  it  also,  but  not  in  such  large  quantities. 
It  has  a  composition  stone,  18  in.  diameter  by  2  in.  face,  and  it  has 
been  very  popular  with  the  shop  men  for  several  reasons.  In  the 
first  place,  it  is  very  simple  and  can  be  taken  apart  and  put 
together  very  easily.  It  also  has  a  hand  wheel  for  turning  the 
lenses,  which  is  very  convenient  when  in  a  hurry,  to  grind  off  any 
bunches  on  the  lens,  if  not  properly  cut.  The  Acme  and  Simplex 
have  a  hand  wheel  for  the  same  purpose. 

The  "Monarch"  is  a  machine  of  medium  size,  not  as  large  as 
the  Gem  or  as  small  as  the  Simplex.  It  has  a  16-inch  composition 
stone  with  either  ij4  or  iJ/2-inch  face  and  requires  only  a  quarter 
or  a  sixth  h.  p.  to  operate.  This  machine  will  edge  from  one 
single  lens  to  as  many  as  will  occupy  the  width  of  the  stone,  all 
lenses  being  constantly  kept  on  the  stone.  Tlie  stone  can  be  tipped 
back  out  of  the  trough  when  desired.  The  machine  can  be  used 
on  the  bench  or  separately  with  stand  or  legs. 

Whichever  machine  you  decide  on  be  sure  to  get  a  composi- 
tion stone,  as  a  Craigleith  requires  constant  care  and  never  works 


The  Making  of  a  Mechanical  Optician  3 

as  satisfactorily.  These  composition  stones  are  very  hard,  and  will 
keep  in  shape  sometimes  for  years.  Either  size  is  all  right  for 
hand  work.  We  might  state  that  it  is  really  better  to  have  a 
separate  stone  for  hand  work,  as  it  enables  you  to  keep  your 
frameless  machine  in  better  condition.  In  grinding  over  a 
machine  the  water  runs  ofif  the  hands  on  to  the  machine.    This  is 


Fig.    1 — Reception  room  and  modern   workbench 


full  of  grit,  and  unless  you  clean  the  machine  every  day  it  will 
soon  become  gummed  up  and  in  time  refuse  to  work.  If  you 
install  the  Simplex,  however,  you  should  have  an  extra  stone, 
which  can  be  obtained  for  about  fifteen  dollars.  The  Simplex  is 
designed  particularly  for  prescription  work.  The  stone  is  but 
10  in.  diameter  and  i  in.  face.  The  machine,  however,  is  built 
just  as   heavy   as   the   large   ones,   and   particular   attention   has 


4  The  Making  of  a  Mechanical  Optician 

been  given  to  the  wearing  qualities.  The  idea  of  using  this  small 
stone  is  to  take  up  less  space  and  to  require  less  power  (a  i/6  h.  p. 
motor  will  operate  it),  and  then  the  stone  can  be  replaced  at  a 
small  cost.  Another  advantage  is  in  case  of  repairs  it  can  be 
boxed  easily  and  shipped  to  the  factory  at  a  small  expense.  This 
will  be  appreciated  by  anyone  having  had  occasion  to  renew 
broken  parts  or  turn  up  a  stone  on  a  large  machine.  Frequently 
it  has  been  necessary  to  pay  a  man's  expenses  from  the  factory 
or  jobbing  house  to  do  this  work,  or  if  the  machine  has  to  be 
sent  to  the  factory  it  must  be  crated  and  shipped  by  freight. 

The  selection  of  one  of  these  machines  will  depend  on  the 
circumstances  and  requirements  of  your  work.  It  should,  how- 
ever, be  placed  at  the  right  hand  end  of  your  bench,  as  you  vvilj 
find  it  more  convenient.  There  are  many  good  drills  on  the 
market,  and  samples  of  these  can  be  seen  at  all  the  large  jobbers, 
or  a  good  idea  of  them  can  be  obtained  by  consulting  the  different 
catalogues.  You  can  obtain  a  low-priced  diamond  drill,  without  a 
centering  device,  that  does  excellent  work,  but  requires  more 
experience  in  centering  the  lenses.  There  is  a  separate  centering 
device  on  the  market  that  can  be  obtained  for  a  small  sum. 
Opticians  having  old-style  drills  will  find  this  a  great  convenience 
in  marking  lenses  for  drilling,  as  it  centers  them  instantly  and 
accurately.    It  also  has  a  scale  for  drilling  above  and  below  center. 

If  you  can  afford  it,  we  should  recommend  a  drill  with  the 
centering  device  and  also  an  arrangement  for  drilling  torics,  such 
as  the  Universal  (Standard  Optical  Company's)  or  the  American 
Optical  Company's  drill.  You  should,  by  all  means,  use  a  diamond 
point,  although  these  are  not  guaranteed.  With  a  little  instruction 
and  by  using  care  you  will  seldom  break  one.  In  selecting  the 
diamond  we  would  recommend  a  white  splint,  as  this  has  a  rough 
point  and  cuts  faster.  It  also  can  be  sharpened  at  less  expense. 
If  you  break  it,  you  can  replace  it  for  about  five  dollars.  The 
turned  diamond  can  be  had  in  white  stones  or  black  carbon,  and 
these  cost  from  twelve  to  eighteen  dollars.  These  are,  perhaps, 
less  liable  to  break,  but  do  not  cut  as  fast.  (In  reality,  they  grind 
a  hole.)  They  cost  more  to  sharpen,  besides  having  to  be  done 
oftener. 

Next  is  the  cutter,  and  this  should  be  placed  on  a  square 
board,  so  that  it  can  be  moved  back  out  of  the  way  when  not  in  use. 


The  Making  of  a  Mechanical  Optician  5 

There  are  only  four  on  the  market,  which  are  used  to  any  great 
extent,  and  these  are :  The  American  Optical  Company ;  Little  Gem 
(Bausch  &  Lomb  Optical  Company)  ;  Standard  and  Globe.  The 
American  Optical  Company's  is  arranged  so  that  most  of  the  dif- 
ferent shapes  and  sizes  can  be  cut  by  adjusting  the  micrometer 
head  according  to  a  scale  furnished  with  the  machine.  The  Stand- 
ard is  operated  by  one  large  pattern  with  a  groove  in  the  under 
side.     In  place  of  a  micrometer  there  is  a  five-sided  barrel  with 


Fig.    2 — A   modern    optician's    workbench 


the  two  rolls  that  run  in  the  groove  in  the  pattern  arranged  at 
different  distances,  so  that  by  turning  it  you  can  cut  the  shapes, 
having  a  difference  between  the  length  and  width  of  ten,  nine, 
eight,  seven  and  six  millimeters.  This  machine  is  furnished  with 
a  steel  wheel,  but  it  can  be  obtained  with  a  diamond,  by  pay- 
ing extra. 

The  little  Gem  has  an  adjustable  pattern,  and  by  adjusting 
both  the  pattern  and  micrometer  head,  according  to  a  chart  fur- 
nished with  it,  you  can  cut  most  all  the  ovals.     While  this  scale 


6  The  Making  of  a  Mechanical  Optician 

is  nearly  right,  we  would  suggest  that  you  make  a  scale  of  your 
own,  for  the  regular  shapes,  for  accurate  work.  This  can  be  done 
by  cutting  old  lenses  and  measuring  them  until  you  find  just  the 
right  amount  to  allow  for  grinding.  The  Globe  is  arranged  by  a 
series  of  patterns,  so  that  it  will  cut  any  size  or  shape.  These  are 
changed  instantly  by  lifting  the  top  gear.  It  has  a  micrometer, 
arranged  with  a  pointer,  so  that  the  frameless  sizes  are  read  in 
millimeters,  and  the  frame  sizes  in  the  regular  way,  i,  o,  oo,  etc. 
This  scale  is  also  arranged  so  that  it  is  set  for  regular  and  full  eye, 
without  any  difficulty,  and  without  consulting  a  chart.  To  cut  a 
lens  40  X  2,3)  subtract  the  width  from  the  length  (this  is  seven 
millimeters).  By  placing  No.  7  pattern  in  the  machine  and  setting 
the  pointer  at  40  mm.,  you  get  the  required  size.  These  patterns 
also  interchange  with  those  on  Acme  and  Simplex  machines. 
This  you  will  find  very  convenient. 

Just  here  we  will  put  in  a  word  about  diamonds.  Quite  fre- 
quently we  hear  that  someone  wants  a  cutting  diamond  sharpened. 
This  is  impossible,  as  a  cutting  stone  is  a  natural  formation,  and 
although  it  can  be  reset  many  times,  it  cannot  be  sharpened.  In 
resetting,  the  stone  is  taken  out  of  the  mounting,  and  reset  at  a 
different  angle.  These  stones  have  from  one  to  four  cutting 
points,  and  after  it  has  been  reset  two  or  three  times,  using  the 
same  point,  it  is  then  necessary  to  find  a  new  point.  Drills  are 
made  of  splints,  which  are  obtained  by  cleaving  large  stones,  or 
from  natural  stones,  sharpened  or  lapped,  by  hand.  These  can  be 
resharpened  a  number  of  times,  and  should  be  kept  sharp  to  do 
quick  work.  The  bench  should  be  equipped  with  a  buff-head, 
having  a  taper  screw  and  chuck,  for  small  drills,  burrs,  polishing 
wheels,  etc.  As  these  are  not  furnished  with  the  outfit,  and  they 
must  be  selected  separately,  we  would  recommend  the  following: 
About  si.x  small  twist  drills,  of  different  sizes,  including  the  size 
for  frameless  glass  screws  and  stud  screws ;  two  sizes  of  solder 
burrs,  for  burring  out  eye  wire  after  soldering;  two  sizes  of 
temple  burrs  for  burring  the  joints  of  temples;  a  brush  wheel;  a 
felt  wheel,  about  three  or  four  inches  diameter,  will  do;  a  cotton 
wheel,  about  six  inches  diameter.  This  outfit  will  do  all  the  work 
you  are  required  to  do. 

Next  is  the  motor,  and  the  first  thing  to  do  is  to  inquire  of 
the  power  company  what  the  current  is.  It  probably  will  be  either 
direct,  no  volts,  or  alternating,  no  volts,  60  cycles,  and  in  asking 


The  Making  of  a  Mechanical  Optician  7 

for  quotation,  or  ordering  an  outfit  from  the  jobber,  be  sure  and 
give  this  information,  as  it  makes  about  twelve  or  fifteen  dollars' 
difference  in  price.  All  quotations  are  given  with  direct  current, 
and  the  alternating  costs  extra.  If  you  have  a  direct  current,  a 
14  h.  p.  shunt-wound  motor  should  be  used.  This  maintains  its 
speed  without  the  load,  while  a  series-wound  will  speed  up  and  the 
load  must  be  kept  on  to  hold  it  down.  You  should  see  that  you 
get  a  quiet  one,  as  a  magnetic  hum  is  very  disagreeable.    There  is 


Fig.    3 — Outfit   for   prescription   \vork 


a  rheostat,  or  starting  box,  furnished  with  it,  and  if  the  outfit  is 
bought  complete  it  will  be  wired  up  on  the  bench  with  a  switch 
and  cut-out.  It  is  only  necessary  then  for  the  electrician  to  con- 
nect the  wires,  and  you  are  ready  to  start. 

If  you  have  alternating  current,  we  should  recommend  an 
automatic  starting,  %  h.  p.  This  requires  no  starting  box,  which 
is  quite  large  for  this  current,  and  is  also  started  quicker.  In 
buying  a  motor,  the  speed  is  an  important  matter,  and  many  of  the 
shops  that  have  been  fitted  up  by  opticians  themselves  are  equipped 
with  high-speed  motors.     These  have  been  installed,  either  from 


8  Tlie  Making  of  a  Mcclianical  Optician 

inexperience,  or  on  account  of  the  low  price.  A  slow  speed  motor 
runs  with  less  noise  and  there  is  less  slipping  of  the  belts.  Then 
again  you  do  not  require  such  large  pulleys.  They  are,  of  course, 
higher  in  price,  but  are  worth  the  difference.  In  belting  up  the 
motor,  an  endless  belt  should  be  used,  so  there  will  be  no  pounding 
of  the  lacing  and  no  vibration.  This  is  very  important,  if  you 
want  a  smooth  running  outfit. 

We  have  now  given  you  a  general  idea  of  the  outfit,  and  we 
think  you  will  see  that  it  is  a  great  deal  better  to  purchase  this 
complete  and  obtain  the  benefit  of  the  experience  of  the  optical 
machinery  manufacturers.  They  have  made  a  study  of  shop 
troubles,  and  have  succeeded  in  eliminating  many  of  them.  Occa- 
sionally you  find  an  optician  who  has  built  his  own  bench,  with 
the  idea  of  saving  money,  but  in  the  end  he  finds  it  has  cost  more 
than  any  first-class  outfit  on  the  market. 

Now  in  regard  to  tools.  These,  of  course,  are  not  furnished. 
You  will  need  the  following:  A  pair  of  breaking  tongs,  cribbers, 
a  hand-diamond,  a  set  of  the  brass  patterns  for  cutting  odd 
lenses,  round-nose  pliers,  snipe-nose  pliers,  optician's  hollow  chop 
pliers ;  flat-nose  pliers,  strap  pliers,  angling  pliers,  cutting  pliers 
(and  as  there  are  plenty  of  special  pliers  on  the  market  we  would 
suggest  looking  them  over  and  getting  a  few  of  the  best  ones) ; 
an  assortm.ent  of  files,  including  rat-tail ;  a  millimeter  rule ; 
broaches,  drilling  fluid,  bifocal  cement  and  polishing  material. 

This  covers  most  of  the  necessary  tools,  and  can  be  added  to 
as  occasion  requires.  When  the  outfit  comes  to  you,  it  will  be 
crated,  and  after  it  is  opened  up.  set  in  place  and  connected  with 
the  current,  it  should  be  wiped  up  to  take  off  the  grease  which  is 
put  on  to  keep  it  from  rusting  in  transit.  Then  look  at  the  bear- 
ings, especially  the  boxes  on  the  stone  and  main  shaft.  These 
may  have  been  set  up  tight  in  shipping.  If  so,  the  screws  should 
be  loosened  a  little  until  they  turn  freely. 

Everything  should  then  be  well  oiled  and  then  the  motor  can 
be  started.  It  should  be  run  a  few  hours,  feeling  the  bearings 
occasionally  to  see  that  they  do  not  warm  up.  If  so,  they  should 
be  loosened  up  a  little  more.  Possibly  the  belts  may  be  a  little 
loose,  and  even  if  they  are  all  right  at  first  they  will  have  to  be 
shortened  later,  as  all  new  belts  will  stretch.  If  the  motor  is  a 
good  one  it  will  have  an  adjustable  base,  so  that  it  can  be  adjusted 
to  take  up  the  slack.    After  taking  up  all  you  can  in  this  way,  have 


The  Making  of  a  Mechanical  Optician  9 

a  piece  taken  out  at  some  belt  manufacturer's,  and  do  not  attempt 
to  lace  it.  All  other  flat  belts  will  be  laced,  however,  and  these 
you  can  take  up  yourself,  but  always  use  light,  thin  lacings  to 
make  it  run  as  smoothly  as  possible.  The  round  belts  will  prob- 
ably be  put  together  with  hooks,  and  they  will  require  shortening 
very  often.  In  shortening  belts  do  not  get  them  too  tight;  it  is 
better  to  run  them  a  little  loose,  and  if  they  slip  it  is  probably  be- 
cause they  are  too  hard  and  dry.  By  applying  a  little  castor  oil, 
occasionally,  on  the  inside,  while  it  is  running,  it  will  make  them 
soft  and  pliable.    Never  use  resin  or  anything  of  that  nature. 

After  everything  is  running  smoothly,  you  can  then  put  water 
on  the  stone  and  place  some  thick  lenses  in  the  machine  and  allow 
them  to  grind  a  while.  In  starting  a  new  composition  stone,  it 
will  absorb  the  water  very  quickly,  and  for  the  first  hour  or  so 
watch  it  carefully  and  see  that  it  does  not  run  dry,  as  this  will 
rough  it  up  and  may  require  turning.  The  stone  can  be  kept  wet 
by  a  drip,  either  from  a  tank,  or  it  can  be  connected  with  the  water 
supply,  but  you  should  then  arrange  for  the  outlet,  or  it  is  liable 
to  overflow.  A  very  popular  way  is  to  have  a  sponge  pan  on  the 
back,  filled  with  water,  and  the  sponge  will  act  as  a  wick,  keeping 
just  enough  water  on  the  stone.  Some  of  the  machines  are  sup- 
plied with  this  sponge  pan  and  we  recommend  this  method,  as  it  is 
much  cleaner.  Some  of  the  stones,  shipped  from  the  factory,  are 
not  quite  ready  to  grind  on,  but  by  running  thick  lenses  in  the 
machine  for  a  while  it  will  smooth  up  very  quickly.  If  it  does  not, 
a  piece  of  the  same  material,  held  by  the  hand,  will  polish  it. 

All  the  frameless  machines  are  equipped  with  truing  devices, 
and  it  is  well  to  true  the  stone  up  every  little  while  to  keep  it  in 
perfect  condition,  rather  than  allow  it  to  get  badly  out,  as  it  is  then 
quite  a  job  to  get  it  back.  All  that  is  necessary  to  do  is  to  set  the 
truing  device  up  until  the  carborundum  stone  just  touches  the 
grindstone  and  allow  it  to  run  a  few  minutes  until  you  cannot 
hear  it  grind.  As  the  stone  oscillates  it  trues  itself  automatically. 
If  your  stone,  for  any  reason,  should  get  badly  out  of  true,  you 
should  turn  it  with  a  carbon  or  black  diamond,  or  you  can  use  the 
new  tool  on  the  market  similar  to  a  carbon.  This  is  placed  in  the 
truing  device  and  operated  the  same  as  the  carborundum  block. 
After  you  have  turned  it  true,  it  will  be  very  rough;  then  by 
replacing  the  carborundum  you  can  smooth  it,  the  same  as  before 
described. 


lO  The  Making  of  a  Mechanical  Optician 

We  will  describe  the  use  of  the  drill  and  cutter  later,  but  they 
can  be  tried,  and  if  they  do  not  suit  have  them  exchanged  at  once, 
as  they  are  not  guaranteed.  Do  not  spoil  them  and  then  claim 
they  were  never  right.  If  you  do  not  get  good  results  in  cutting, 
it  is  probably  because  you  have  not  used  just  the  right  pressure. 
Start  lightly,  and  on  each  lens  gradually  increase  the  pressure 
until  you  get  a  good  clean  cut. 

The  cost  of  operating  is  trifling,  as  a  %  h.  p.  motor  uses  very 
little  current,  costing  not  over  one  dollar  a  month. 

The  illustrations  shown  on  the  preceding  pages  will  give  an 
idea  of  the  arrangement  of  the  benches  most  in  use. 


CHAPTER  II 


CARE  OF  MACHINERY 

Machinery  may  have  the  best  of  care,  but  it  needs  a  thorough 
overhauHng  about  once  a  year.  Many  opticians,  especially  those 
having  the  new  style  benches,  are  very  particular  to  keep  them 
clean,  and,  although  their  intentions  are  good,  this  is  often  the 
cause  of  trouble.  A  machine  that  is  running  constantly  in  water 
needs  considerable  oil,  and  although  a  machine  covered  with 
grease  does  not  look  very  neat,  it  is  really  the  most  practical.  If 
the  machine  is  not  wiped  carefully  the  water  and  grit  are  deposited 
on  the  metal,  which  causes  it  to  rust  or  bind  very  quickly. 

The  proper  method  for  the  care  of  a  frameless  machine  is 
to  wipe  off  carefully  the  water  and  grindstone  grit,  but  see  that 
.  it  is  pretty  well  covered  with  oil.  All  machines  are  supplied  with 
oil  cups,  and  these,  if  kept  well  filled,  will  take  care  of  the  bear- 
ings to  a  certain  extent,  but  all  bright  parts  exposed  should  be 
well  oiled  also.  This  includes  the  gears,  shafts  and  all  working 
parts.  The  grindstone  grit,  which  is  a  mixture  of  glass  and 
stone,  is  partly  the  cause  of  trouble  and  allowing  the  bearings  or 
shafts  to  run  dry  is  usually  responsible  for  the  rest. 

A  machine  that  has  the  best  of  care  will,  after  a  time,  run 
hard,  and  as  soon  as  this  is  noticed  it  should  be  taken  apart  and 
the  trouble  located.  The  first  symptom  is  that  a  great  deal  of 
spring  tension  is  needed  to  hold  the  lenses  against  the  stone.  This 
may  be  noticed  on  account  of  the  lenses  not  grinding  very  quickly, 
or  that  the  lenses  have  a  tendency  to  pull  away  from  the  stone. 
If,  for  anv  reason,  this  may  have  escaped  the  operator's  attention, 
the  machine  will  gradually  get  worse,  an<l  suddenly  it  will  pull 
back  and  forth  from  the  stone.  This  will  cause  the  .lenses  to  slip, 
and  possibly  to  chip  or  break.  This  motion  is  caused  by  friction 
and,  by  studying  the  transmission  a  moment,  it  is  easily  under- 
stood. The  shaft  or  belt,  whichever  way  the  machine  may  be 
constructed,  is  arranged  so  the  lower  shaft  turns  in  the  opposite 
direction  to  the  stone,  and  the  .small  gears  on  this  shaft  mesh  with 
the  larger  ones  on  the  upper  shafts.    The  upper  .shafts  must  neces- 


12  The  Making  of  a  }[cciiaiiical  Optician 

sarily  revolve  in  the  opposite  direction  from  the  lower  shafts,  or 
toward  the  stone.  If  there  is  friction  anywhere  on  the  lower 
shaft  it  has  a  tendency  to  cause  the  upper  shafts  to  revolve  in  the 
same  direction  as  the  lower,  and,  consequently,  it  turns  as  far  as 
the  spring  will  allow  it,  and  then  jumps  backward. 

The  first  step  is  to  locate  which  shaft  is  the  cause  of  the 
trouble.  By  removing  the  small  gear  on  the  left  side  of  the  lower 
shaft,  it  will  leave  the  upper  one  on  the  left  free.  As  this  par- 
ticular one  has  either  a  ball  bearing  or  a  cone  bearing,  there  may 
be  trouble  at  this  point.  If  the  difficulty  is  located  in  this  shaft. 
the  remainder  of  the  machine  can  be  turned  with  the  hand  wheel. 
If  it  turns  freely,  it  will  not  be  necessary  to  take  any  more  of 
the  machine  apart,  unless,  possibly,  you  may  intend  to  give  the 
machine  a  thorough  overhauling.  The  shaft  that  is  the  cause 
of  the  trouble  must  be  removed  and  thoroughly  cleaned.  If  it  is 
simply  gummed  up  with  grease,  this  can  be  removed  with  kero- 
sene, but  if  the  shaft  has  been  running  dry,  and  this  is  the  most 
common  trouble,  it  is  probably  scored  so  that  it  binds.  A  fine 
grade  of  emery  cloth  should  be  used  to  smooth  it.  rubbing  it  down 
until  it  fits  easily.  Before  it  is  replaced  the  bearing  should  be 
cleaned  thoroughly  with  kerosene  and  the  oil  hole  or  cup  cleaned. 

A  machine  may  be  oiled  regularly,  but  oftentimes  the  oil  be- 
comes gummed,  stopping  up  the  oil  cup,  and  yet  escapes  the  atten- 
tion of  the  operator.  If  it  is  the  lower  shaft  that  is  causing  this 
trouble,  there  is  nothing  more  to  do  to  it,  but  should  it  be  either 
of  theiipper  shafts,  the  ball  or  cone  bearings  must  be  looked  over 
carefullw  If  anv  of  the  balls  are  broken,  replace  them  as  soon  as 
possible,  although  the  machine  can  l)e  run  temporarily  with  one  or 
two  missing.  If  it  is  a  cone  bearing,  it  may  ha\e  become  worn 
or  scored  a  little  and  may  need  to  be  turned.  If  the  machine  is 
one  that  has  a  screw-clamping  arrangement  for  holding  the  lenses, 
this  will  have  to  he  taken  apart  and  looked  over  carefully :  it  may 
be  only  gummed  up  or  a  spring  may  be  1)ri)ken,  which  will  have 
to  be  replaced. 

.A  machine  that  has  Iieen' running  one  year  will  show  little 
or  no  wear,  Init  if  it  has  been  running  for  a  longer  period,  the 
bearings  niav  be  considerably  worn.  In  this  case  they  .should  be 
fitted  with  new  shafts  and  bushings,  and  if  one  is  to  have  accurate 
work  there  can  be  no  great  ainimnt  of  jilay  in  the  bearings.     It 


The  Making  of  a  Mechanical  Optician 


13 


will  depend,  however,  on  the  machine ;  if  it  is  so  constructed  that 
the  pattern  is  near  the  lenses,  the  wear  does  not  make  as  much 
difference  as  if  it  were  placed  on  the  other  end  of  the  shaft.  If 
a  machine  needs  repairing,  the  front  part  can  be  removed  and 
shipped  to  the  factory,  by  express.  It  is  unnecessary  to  ship  the 
stone,  stand,  etc.,  unless  one  is  not  mechanically  inclined.  When 
it  comes  to  a  question  of  repairs,  it  is  cheaper  and  better  to  send 
it  to  the  factor)-  where  it  is  manufactured,- as  they  have  the  parts 
in  stock  and  understand  what  is  required  better  than  some  local 
machinist. 

After  the  machine  is  in  running  order  again,  there  are  some 
points  which  should  be  looked  after  to  put  the  machine  in  first- 
class  condition.  The  bearings  of  the  stone  will  probably  show 
signs  of  wear  and,  as  all  the  best  machines  are  constructed  with 
split  boxes,  all  that  is  necessary  to  do  is  to  tighten  the  four  set 
screws  occasionally,  to  take  up  the  play   (Fig.  4).     .-V  bearing 


Fig.  4 


of  this  kind  is  babbitted — that  is,  it  is  lined  with  a  composition 
of  soft  metal,  consisting  of  lead,  tin  and  antimony.  This  forms 
one  of  the  most  satisfactory  bearings,  although  not  the  best  or 
most  expensive.  The  theory  is  that  one  soft  metal  and  one  hard 
metal,  running  together,  cause  the  least  friction  and  the  least  wear. 
When  a  bearing  of  this  description  is  made,  the  soft  metal  is 
poured,  when  hot,  into  the  cast-iron  box  around  the  .shaft,  so  that 
it  is  shaped  to  it  perfectly.  It  is,  however,  left  a  little  large, 
to  allow  for  a  "take  up''  as  the  bearing  wears.  After  the  wear 
has  been  taken  up  as  much  as  possible  the  boxes  mu.st  be  re- 
babbitted  :  this  can  be  done  by  any  local  machinist.     To  obtain 


14 


The  Making  of  a  Mechanical  Optician 


the  best  results  in  lens  grinding,  these  bearings  should  be  kept  in 
shape,  although  they  can  be  run  for  years  with  loose  boxes  with- 
out much  serious  trouble.  When  the  stone  is  to  be  turned  is 
where  the  greatest  trouble  will  be  found,  as  it  is  impossible  to 
turn  it  true  if  there  is  any  "play"  in  the  boxes. 

The  stone  at  this  time  may  need  turning,  possibly  on  account 


Fig.  5 


of  ridges  near  the  edges,  caused  by  the  lenses  not  covering  the 
entire  surface  of  the  stone.  The  truing  device  is  supposed  to  take 
care  of  this  wear,  but  this  device  is  usually  neglected  by  most 
opticians.  The  correct  way  is  to  set  this  up  to  the  stone  every 
day  for  a  few  minutes,  to  offset  the  amount  of  wear  caused  by 
the  grinding.  If  it  is  used  only  occasionally,  it  requires  quite  a 
little  time  to  put  the  stone  in  first-class  shape  with  this  device, 
consequently  the  most  satisfactory  way  is  to  turn  the  surface  off 
.squarely  with  a  diamond  and  then  finish  it  with  a  truing  device. 
This  operation  was  described  earlier  in  this  chapter.  If  the 
surface  of  the  stone  shows  no  signs  of  w-ear  it  still  may  need 
turning,  on  account  of  it  being  out  of  round.  This  will  make  no 
great  difference  in  hand  grinding,  but  in  machine  work  it  will 
cause  ridges  or  facets  to  appear  on  the  edges  of  the  lenses  (Fig. 
6).  \\"hen  this  defect  is  found,  many  grinders  look  for  trouble 
in  some  part  of  the  machine,  but  this  is  always  caused  by  the 


The  Making  of  a  Mechanical  Optician  15 

stone  being  out  of  round.     As  stated  before,  it  is  impossible  to 
turn  it  perfectly  true  unless  the  bearings  are  in  perfect  condition. 

After  a  stone  has  been  turned  a  number  of  times  the  gage 
controlling  the  size  of  lenses  will  need  adjusting,  to  allow  for 
the  reducing  in  size  of  the  stone.     Every  machine  is  constructed 
so  that  this  adjustment  is  very  simple.    All  that  is  neces- 
sary is  to  grind  a  lens  with  the  gage,  set  at  any  size,  and, 
when  it  is  finished,  measure  it  accurately  with  a  rule.    The 
gage  or  pointer  should  then  be  loosened  and  set  to  this 
size.    By  consulting  the  directions  which  accompany  each 
machine,  anyone  can  easily  set  his  machine  without  any 
difficulty. 

The  contact  block,  on  which  the  pattern  or  former 
rides,  also  may  show  signs  of  wear.  This,  as  it  becomes 
grooved,  will  change  the  shape  of  the  lenses,  although  they 
will  not  be  exactly  like  the  patterns  used.  This  makes  no 
particular  difference  when  grinding  pairs,  but  when 
matching  an  old  lens  they  will  not  be  alike.  On  some  p;  g 
machines  it  will  be  necessary  to  fit  a  new  plate,  and  on 
others  the  block  can  be  reversed.  After  both  sides  are  worn  a 
new  one  then  should  be  fitted. 

We  will  next  turn  our  attention  to  the  drill.  With  the  usual 
amount  of  work  in  a  small  shop,  this  should  require  very  little 
repairing.  The  upright  spindle  will  wear  for  years,  but  possibly 
the  idler  shaft  and  idlers  may  have  become  worn  so  they  rattle. 
This  does  no  particular  harm,  except  that  the  noise  is  objection- 
able. Any  local  machine  shop  can  bush  these  bearings  at  a  slight 
expense  and  it  is  well  worth  the  trouble  and  expense  to  eliminate 
the  noise.  The  centering  device  may  require  some  attention,  as 
this  is  operated  in  grit  most  of  the  time.  With  only  a  slight 
amount  of  wear,  this  can  be  taken  up  in  a  machine  shop  or  at  the 
factory,  but  when  it  gets  very  loose  it  is  better  to  exchange  the 
whole  machine  for  a  new  one,  paying,  of  course,  the  difference 
in  cost.  Any  good  drill  should  wear  for  years,  however,  before 
this  part  will  cause  trouble.  After  drilling  for  six  months  or  a 
year,  the  diamond  should  be  repointed.  Many  are  using  slow- 
cutting  drills,  in  ignorance  of  the  fact  that  they  can  be  sharpened 
at  a  slight  expense,  and  these  drills  not  only  exhaust  the  patience, 
but  also  may  break  lenses,  on  account  of  the  unnecessary  pressure 
required. 


i6 


The  Making  of  a  Mechanical  Optician 


The  cutter  should  require  no  repairing,  except  possibly  the 
diamond  may  need  resetting.  Do  not  confuse  a  diamond,  used 
for  cutting,  with  a  drill.  A  drill  can  be  sharpened,  but  a  cutting 
diamond  must  have  a  natural  point.     In  resetting,  the  stone  is 


K. 


1 


X       ' 

\  / 


'X         V 


V-> 


r\ 


/^i 


^1   w 


f\' 


ci'T   ^E^ 


Fig.  7 

Showing    method    of    lacing 
2-inch  belt 


-/•  JkLt^ ^ 


Fig.  8 

Showing    method    of    lacing 
1-inch    belt 


taken  out  and  reset  at  a  different  angle  or  so  that  a  new  point 
can  be  used.  When  it  is  necessary  to  have  your  diamond  reset, 
send  it  to  your  jobber,  so  that  it  may  be  done  by  one  familiar 
with  the  requirements  of  a  machine  for  optical  work.  A  regular 
diamond-setter  may  not  have  had  experience  in  the  optical  line, 
consequently  the  best  results  are  not  obtained. 

The  buft  head  will  probably  need  to  be  taken  up  in  the  bear- 
ings.   This  is  not  necessary,  e.xcept  that  it  may  rattle  so  the  noise 


The  Making  of  a  Mechanical  Optician 


17 


is  objectionable.     This  machine   is   also   constructed   with    split 
bearings,  so  they  can  be  taken  up. 

The  motor  should  require  no  attention  for  some  time.  After 
a  while  the  carbon  brushes  will  wear  down,  so  that  it  will  be 
necessary  to  replace  them.  These  cost  but  very  little  and  can  be 
obtained  from  anv  motor  dealer.  After  some  years  the  part  of 
the  armature  called  the  "commutator"  will,  perhaps,  become 
worn  from  contact  with  the  brushes.  When  this  is  worn  to  any 
great  extent,  it  should  be  sent  to  a  motor  repairer,  who  can  turn 
this  oH  in  a  lathe.  The  ordinary  care  of  a  motor  requires  regu- 
lar oiling  and  occasionally,  in  the  event  of  sparking,  the  commu- 
tator can  be  cleaned  or  smoothed  with  a  piece  of  00  sand  paper. 
Occasionally  a  little  vaseline  on  the  tip  of  the  finger  and  rubbed 
on  the  commutator  while  running  will  stop  any  sparking. 

The  bearings  on  the  main  shaft,  and  also  any  countershafts, 
should  be  looked  over  and  any  wear  taken  up  by  tightening  the 
set  screws.  If  any  belts  are  slack,  they  should 
be  tightened.  Small  flat  belts,  or  those  driving 
the  stones,  can  be  laced.  There  are  several 
methods  of  connecting,  but  rawhide  lacings  are 
the  most  satisfactory,  as  they  lie  flat  and  are 
practically  noiseless.  Hooks  and  metal  connec- 
tions make  a  click,  which  is  objectionable. 

In  lacing  a  belt,  three  small  holes  should 
be  punched  on  each  end,  then  two  more  in  a 
line  at  a  reasonable  distance  back  of  them 
I  Fig.  6).  The  lacing  should  be  thin  and  passed 
through  the  holes  as  shown  in  the  illustration. 
Round  belts  can  be  connected  with  steel  belt 
hooks  (Fig.  7).  When  flat  belts  slip,  pour  a 
little  castor  oil  on  the  inside,  while  running. 
Fig-  9      Never  use  any  other  substance. 

Make  it  a  point  to  keep  your  machinery  in  good  runnhig 
order.  To  have  a  noisy  shop  or  outfit  shows  lack  of  attention 
to  the  small  details.  It  is  just  as  easy  to  have  your  machinery 
run  noiselessly,  and  the  impression  it  will  make  on  your  patrons 
is  well  worth  the  trouble. 


J 


I 


Fig.  10 


CHAPTER  III 


LENSES— MARKING  AND   CUTTING 

In  selecting  the  stock  of  lenses  quite  a  little  capital  can  be 
invested,  or  you  can  start  small  and  increase  it  from  day  to  day. 
A  stock  varies  in  price  from  $50  to  $500,  but  the  usual  amount 
invested  is  from  $100  to  $200.  This  will  include  principally  -{-  3 
+  compounds,  a  few  —  3  — .  piano  cylinders,  oval  or  round 
Dcx.  and  Dec.  sphericals,  Pcx.  sphericals,  regular  and  piano 
wafers.  If  you  use  large,  full  eye  lenses  it  will  be  better  to  have 
the  sphericals  in  round,  as  these  will- grind  40  mm.  or  41  mm.  in 
length  and  any  width.  The  +3  —  and  —  3  +  compounds, 
compound  wafers  and  rough  cylinders  (provided  you  are  to  do 
surface  grinding),  can  be  ordered  daily,  until  you  can  afford  to 
stock  them. 

Compounds  are  put  up  in  single  envelopes,  with  the  axes 
dotted,  cylinders  in  packages  of  half  dozen  pairs,  the  axes  dotted, 
and  sphericals  in  the  same  way,  but  not  dotted.  By  this  you  will 
see  that  it  is  better  to  buy  cylinders  and  sphericals  in  original 
packages,  although  compounds  can  be  ordered  three  pairs  of  a 
number.  If  you  have  had  no  previous  experience  in  ordering,  a 
good  plan  is  to  see  your  jobbers  and  tell  them  that  you  wish  to 
place  an  order  for  a  quantity  of  rough  lenses,  stating  the  amount 
you  wish  to  invest,  and  let  them  submit  lens  sheets,  showing  the 
assortment  and  quantities  that  can  be  obtained  for  this  figure. 
As  they  are  constantly  making  them  up,  they  can  best  advise  you. 
You  can  then  look  it  over  and  change  it  as  you  see  fit.  If  you 
have  made  no  provision  for  carrying  your  stock,  we  would  sug- 
gest getting  an  uncut  lens  cabinet.  This  is  made  of  oak,  with 
galvanized  iron  drawers,  with  wood  front  and  back.  The  small 
drawers  are  partitioned  off  for  compounds  and  the  large  for  cyl- 
inders and  sphericals.  The  latter  have  pressed  paper  partitions  in 
front  for  single  lenses,  without  wrappers,  and  the  surplus  is  placed 
in  the  rear.  This  can  be  obtained  much  cheaper  than  you  can 
have  one  made  and  will  last  a  great  many  years. 

A  good  way  to  keep  your  stock  ordered  up  is  to  have  a  box 

18 


The  Making  of  a  Mechanical  Optician 


19 


handy,  and  as  you  use  the  compounds  put  the  envelopes  into  it  and 
order  from  them. 

In  selecting  the  lenses  for  a  prescription  it  will  be  necessary 
to  have  a  pair  of  calipers  or  lens  gage,  graduated  in  1/5  mm. 
With  this  the  lenses  are  calipered  in  the  center,  allow^ing  2/5  mm. 
for  each  diopter.  For  example,  a  piano  lens  is  the  same  thickness 
on  the  edge  as  in  the  center,  and  if  you  wish  to  make  a  pair  of 
glasses  two-strap  thickness,  having  a  piano  in  one  eye  and  +  i  in 
the  other,  we  select  the  piano  first  2  mm.  thickness  and  tlie  +  i. 
2  2/s  in  the  center.  If  the  lens  was  concave,  it  would  be  i  3/5  mm. 
In  this  way  the  edges  are  made  the  same  thickness.  In  cases 
where  there  is  to  be  a  compound  in  one  eye  and  spherical  in  the 
other,  it  is  well  to  look  at  the  compound  and  use  your  judgment 


Fig.  11 

as  to  which  would  be  best — a  double  convex  or  periscopic.  If  tlie 
compound  is  +  3  +»  a  Dcx.  would  make  a  better  match ; 
whereas  if  it  were  +  Z^  — >  a  Pcx.  would  be  nearer  the  curve. 

For  marking  you  will  need  quite  a  stiff  pen  that  does  not 
scratch,  a  bottle  of  black  waterproof  ink  and  a  protractor  gradu- 
ated in  five  degrees.  These  are  furnished  by  some  jobbers,  as 
advertisements,  with  3  decentering  scale  on  the  back,  which  is 
very  convenient.  For  cross  lines  use  a  card  about  the  size  of  a 
reading  test  type,  and  draw  heavy  black  lines  at  90°  and  180°. 
This  will  be  used  for  medium  and  strong  powers ;  for  the 
weak  powers  draw  the  lines  on  a  wall  about  twenty  feet  dis- 
tant. In  marking,  first  decide  which  surface  will  be  next  the  eye 
and  then  always  mark  on  this  surface.     The  rule  is,  the  greatest 


20 


The  -Vakiiig  of  a  Mechanical  Optician 


concavity  or  the  least  convexity,  next  to  the  eye,  always  having 
the  cylinders  on  the  same  side,  except  in  extreme  cases.  We  will 
first  select  a  sphere,  and  all  that  is  necessary  in  this  case  is  to  dot 


the  center.     We  find  the  center  by  looking  through  the  lens  at 
crossed  lines,  and  the  lines  will  appear  broken  (Fig.  ii  ). 

Then  move  the  lens  until  the  lines  are  continuous  and  place  a 


Fig.  13 

dot  where  the  lines  cross  (Fig.  12).     A  cylinder  usually  has  the 
axis  running  from  corner  to  corner,  and  in  lining  it  up  the  lines 

will  appear  broken  and  perhaps  twisted  (Fig.  13).   By  turning  the 
lens  they  will  line  up  so  that  they  appear  straight  and  by  moving 


The  Making  of  a  Mechanical  Optician 


21 


in  a  horizontal  and  vertical  position  they  will  be  continuous.  Then 
place  two  dots  on  the  lens,  one  at  the  top  and  one  at  the  bottom. 
Now  lay  it  on  the  protractor  with  these  dots  at  whatever  axis  the 
lens  is  to  be  cut.    Draw  a  line  across  the  lens  at  axis  i8o°.    This 


will  be  the  mechanical  axis  or  cutting  line,  as  it  is  usually  called. 
Remember  that  whatever  axis  is  to  be  cut  the  cutting  line  is 
always  drawn  at  i8o°.  For  example,  axis  45°  will  be  placed,  as 
shown  in  Fig.  14,  axis  90°  as  Fig.  15. 


Fig.  15 

A  compound  is  lined  up  in  the  same  way  as  a  cylinder,  and 
the  lines  will  look  the  same,  but  when  you  have  it  in  position  three 
dots  must  be  placed  on  the  lens,  one  at  the  top,  one  at  the  bottom 
and  one  in  the  center.    It  is  then  laid  on  the  protractor  the  same 


22 


The  Making  of  a  Mechanical  Optician 


way,  but  be  sure  that  the  center  dot  is  on  the  center  of  the  chart 
or  your  lens  will  be  decentered.  If  you  wish  to  obtain  some  pris- 
matic power  you  can  decenter  it,  using  the  following  rule :  A  lens 
decentered  ten  millimeters  will  produce  a  prism  power  of  as  many 
diopters  as  the  focus.  Thus  z  -\-  \  T>.  lens,  decentered  lo  mm., 
will  have  a  prism  power  of  i  D.    By  this  you  will  see  that  a  + 


I  D.  lens,  decentered,  2.5  mm.,  would  give  us  ^  D.  prism.  A 
mistake  is  often  made,  however,  in  ordering  a  lens  decentered  6 
or  8  mm.  This  cannot  be  done,  as  the  stock  lenses  are  not  large 
enough.  Extra  large  lenses  could  be  used,  but  these  would  cost 
more  than  to  have  a  pair  surface  ground.     With  the  large  sizes 


■f-LOD-f/p.S'O 


-h.S'OCul 

Fig.   17 

that  are  now  being  used  a  lens  cannot  be  decentered  over  2  mm. 
In  marking  a  lens  to  be  decentered,  it  is  dotted  in  the  usual  way 
and  then  moved  on  the  chart  the  amount  necessary  and  a  cross 
line  drawn  on  the  cutting  line  (Fig.  16).  Before  the  lenses  are 
cut  they  should  be  neutralized  to  be  sure  the  power  is  correct.  If 
you  depend  on  the  lens  measure  it  should  be  kept  accurate  by 
frequent  adjusting,  and  if  you  do  not  have  two,  one  for  American 


The  Making  of  a  Mechanical  Optician  23 

Optical  Company  and  one  for  Bausch  &  Lomb,  you  should  make 
an  allowance  of  .03  D.  for  every  diopter.  We  prefer  to  use  a  lens 
measure,  graduated  for  Bausch  &  Lomb  stock,  and  then  add  the 
required  amount  when  measuring  American  Optical  Company's 
stock. 

\'ery  little  can  be  saved  in  buying  torics  uncut,  as  the  re- 
sponsibility of  breaking  is  too  great,  but  if  you  prefer  to  grind 
these  yourself  they  are  handled  just  the  same  as  flat  lenses  in 
marking.  We  will  give  a  few  suggestions  for  ordering,  so  that 
you  will  be  sure  to  get  the  best  results.  If  all  prescriptions  for 
torics  were  filled  as  written  a  great  many  would  have  no  toric 
effect. 

You  should,  of  course,  understand  the  transposition  of  lenses, 
and  transpose  them  to  the  best  form  before  sending  in  the  pre- 
scription. If  you  do  not  you  should  state  that  you  want  the  pre- 
scription filled  in  the  best  form.    In  ordering  plain  cylinders  it  will 


i-'^.00  SyoX 


Fig.  18 

make  no  difference  which  way  they  are  ordered,  unless  wafers  are 
to  be  fitted.  If  a  -(-  cylinder  was  ordered,  the  lens  would  be 
ground  as  written  and  would  have  the  cylinder  on  the  outside,  and 
a  6  D.  curve  on  the  inside  (Fig.  17).  If  a  —  cylinder  was  ordered 
it  would  be  ground  with  the  cylinder  on  the  inside  and  a  -}-  6  D. 
curve  on  the  outside  (Fig.  18).  If  wafers  were  to  be  fitted,  the 
cylinder  should  be  on  the  outside,  so  that  the  wafers  could  be 
cemented  to  the  inside  surface.  It  would  then  be  necessary  to 
transpose  to  a  compound.  For  example :  A  —  .50  cylinder,  axis 
180°,  would  be  —  .50  sphere  3  +  -SO  cylinder,  axis  90°.  This 
lens  would,  of  course,  cost  extra. 

The  ordering  of  compounds  is  a  more  difficult  matter  and  the 
optician  should  know  just  what  surfaces  are  to  be  ground.  For 
example:  If  a  +  i  sphere  3  +  -SO  cylinder,  axis  90°,  was 
ordered,  it  would  be  ground  as  written,  and  the  lens  would  be 


24 


The  Making  of  a  Mechanical  Optician 


+  6  ^  +  6.50  on  the  outside  and  a  —  5  sphere  on  the  inside 
(Fig.  19). 

By  this  you  will  see  that  the  toric  effect  has  been  reduced  i  D. 
While  it  does  not  matter  much  in  this  case,  the  toric  effect  is 


Fig.  19 

gradually  reduced  until  with  a  combination  of  +  6  sphere  3  + 
.50  cylinder,  axis  90°,  it  has  a  piano  effect  and  this  would  be 
ground  with  +  63  +  6.50  on  the  outside  and  piano  on  the 
inside  (Fig.  20). 

All  +  and  +  combinations  with  a  spherical  stronger  than  + 
/  should  be  transposed.     For  example:    +  3  sphere  3  +  i  cyl- 

■i-6>.0d^fL6rc> 


Fig.  20 

inder,  axis  90°,  if  ground  as  written,  would  have  only  —  3D. 
inside  curve.  If  it  is  transposed  it  would  be  ground  with  +  10 
D.  outside  and  —  63  —  7  inside  (Fig.  21  ).  This  lens  costs 
more,  but  will  give  better  satisfaction  to  your  customer.     If  you 

9.  c  uri/e. 


Fig.  21 

understand  this  before  ordering  you  can  explain  it  to  your  cus- 
tomer and  charge  more  for  your  lens  accordingly.    Concave  com- 


The  Making  of  a  Mechanical  Optician  25 

binations  are  transposed  in  the  same  way.  When  wafers  are  to 
be  fitted  they  should  be  transposed  so  that  the  cylinders  are  on 
the  outside. 

In  covtbinatio7is  where  the  spherical  power  exceeds  -\-  j,  the 
distance  lenses  should  be  ordered  on  a  -\-  9  curve.    Thus  a  combi- 


-i-V.OO^i- /d.60 


Fig.  22 

nation  +  3  sphere  3  +  i  cylinder  would  be  +  9  C^  10  on  the 
outside  and  —  6  sphere  on  the  inside  (  Fig.  22 ).  This  gives  you 
the  regular  —  6  toric  effect,  and  although  it  increases  the  expense 
it  makes  a  much  better  lens. 


CHAPTER  IV 


MARKING  PRISMS 

Opticians,  as  a  rule,  prefer  sending  their  prism  work  to  the 
prescription  houses ;  some,  however,  purchase  the  lenses  uncut 
and  edge  them  in  their  own  shop.  The  amount  saved  is  trifling 
when  the  risk  of  breakage  is  considered;  still,  many  are  willing 
to  accept  the  responsibility.  A  great  deal  of  care  should  be  used 
in  marking  these  lenses,  especially  with  cylinder  or  sphero  cylinder 
prisms. 

A  piano  prism  must  be  accurately  ground ;  that  is,  the  power 
must  be  perfect,  as  any  decentration  cannot  change  it.    When  the 


'«  IS-  to  IS  ^0 

Fig.  23 


lens  is  selected,  it  is  first  tested  to  ascertain  if  the  power  is  correct, 
either  by  using  a  test  prism  to  neutralize  it,  or  by  sighting  at  a 
prism  chart  (Fig.  23).  This  consists  of  a  series  of  lines,  an 
equal  distance  apart,  graduated  from  J4°  to  30°.  At  whatever 
distance  the  chart  may  be  arranged  for,  the  first  long  line  appears 
to  be  moved  along  the  chart,  indicating  the  power  of  the  prism 
that  is  tested.  This  method  is  convenient,  but  is  used  only  with 
piano  prisms. 

A  piano  prism  will  appear  to  throw  the  line  to  one  side,  the 
same  as  any  lens  out  of  center.  When  twisting  a  piano  prism,  the 
line  does  not  remain  stationary,  as  with  a  spherical,  or  twist,  as 
does  a  cylinder.  The  movement  appears  to  move  the  line  to,  or 
away  from,  the  straight  line,  but  always  parallel  to  it.  To  ex- 
periment, take  a  prism,  hold  it  with  the  base  up  or  down,  and  sight 
at  a  straight  line :  this  you  will  find  will  be  continuous.  Now  turn 
the  prism,  and  the  straight  line  will  move  to  one  side,  until  a 


The  Making  of  a  Mechanical  Optician 


27 


quarter  turn  has  been  made;  this  will  be  the  extreme  point  that 
the  line  will  travel,  and  will  indicate  the  power  of  the  prism.  Now 
continue  in  the  same  direction,  until  another  quarter  turn  has 
been  made,  and  you  will  notice  that  the  line  will  appear  to  move 
back  until  it  is  continuous  again  (Figs.  24,  25,  26).  In  neutral- 
izing, the  test  prism  is  placed  against  the  one  to  be  tested,  and 
when  looking  at  a  straight  line,  it  will  be  continuous. 

When  marking  a  piano  prism,  it  is  held  so  that  the  base  will 
either  be  upward  or  downward.  We  then  sight  at  a  straight  line 
in  the  same  manner  as  a  compound,  but  in  order  to  make  the  line 
continuous  it  must  be  rotated.     Moving  the  lens  sidewa)s  will 


Fig.  24 


not  change  the  lens  in  any  respect.  If  the  lines  are  not  continuous, 
there  will  be  a  prism  power  either  base  upward  or  downward,  as 
well  as  in  or  out.  Having  lined  up  the  lens  correctly,  a  mechanical 
a.xis  or  cutting  line  is  drawn  from  base  to  apex,  provided  the  lens 
is  to  be  fitted  with  the  base  in  or  out.  If  the  base  is  to  be  up  or 
down,  it  must  be  lined  up  and  dotted  in  the  same  manner,  but  the 
mechanical  a.xis  is  drawn  at  right  angles.  As  there  is  no  center 
on  a  piano  prism,  it  does  not  matter  whether  it  is  cut  in  the 
center  of  the  lens,  or  near  the  ape.x  or  base,  except  that  the  thick- 
ness will  vary.  If  a  thin  lens  is  desired,  it  can  be  cut  near  the 
ape.x,  or  thin  edge;  if  a  thick  one,  cut  it  near  the  base,  or  thick 
edge  (Fig.  27 ).  The  one  point  to  bear  in  mind  is,  that  the  power 
does  not  change  as  you  move  the  pattern  by  which  the  lens  is 
cut  up  or  down,  in  or  out,  iirox'ided  it  is  not  twisted. 


28 


The  Making  of  a  Mechanical  Optician 


If  a  piano  prism  is  twisted,  we  immediately  obtain  power  in 
the  opposite  direction  (Fig.  28).  A  chart  is  published  for  the 
purpose  of  computing  double  prisms.  This  is  hot  only  convenient 
for  marking  these  lenses,  but  it  also  tells  us  the  amount  of  prism 


-^ s 

— '         I  d^ 


Fig.  25 


Fig.  26 


obtained  in  both  directions,  when  a  prism  of  any  diopter  is  fitted 
at  any  angle  other  than  90°  or  180°.  For  example,  if  a  2°  prism 
is  fitted  at  axis  45°,  it  will  have  the  effect  of  ij4°  out  and  ij/j"  up; 
or  if  the  prescription  calls  for  2°  in  and  2°  up,  we  can  cut  a  3°  at 
axis  135°.  By  this  method  it  will  be  easily  seen  that  a  slight 
variation  will  produce  a  prism  power  in  the  opposite  direction. 

A  sphero  prism  is  handled  in  much  the  same  manner  as  a 
piano  prism,  except  that  there  may  possibly  be  a  center  on  the 
lens,  and  this  must  be  considered.  A  weak  spherical  with  a  high 
power  prism  will  have  no  center  on  the  lens,  whereas  a  strong 
spherical  with  a  low  power  prism  will  have  the  center  so  near 
the  middle  of  the  lens  that  the  prism  power  can  be  cut  or  ground 
out  very  easily,  and  a  simple  spherical  produced.  A  sphero  prism 
is  nothing  more  or  less  than  a  decentered  spherical,  and  by  refer- 
ring to  the  rule  it  will  be  seen  that  if  a  spherical  lens  is  decentered 
it  will  produce  1°  prism  power  for  every  10  mm.  decentration.  If 
si)hericals  were  large  enough,  it  would  not  be  necessary  to  grind 


The  Making  of  a  Mechanical  Optician 


29 


sphere  prisms,  but  to  produce  the  high  powers  it  would  require 
immense  blanks.  A  spherical  can  be  decentered  a  limited  amount, 
and  tables  are  published  by  the  prescription  houses  for  this  pur- 
pose (Fig.  29),  but  it  is  impossible  to  decenter  any  lens  much 
more  than  2  mm.  Extra  large  lenses  can  be  used,  to  be  sure,  but 
these  also  cost  extra,  so  that  it  is  just  as  cheap  to  use  sphero 
prisms. 

In  marking,  the  lens  is  lined  up  the  same  as  a  piano  prism ; 
that  is,  with  the  base  up  or  down,  and  the  mechanical  axis  drawn 
as  before.  It  is  then  turned  in  the  opposite  direction,  and  a  test 
prism  held  over  it,  of  the  required  pow-er.  A  short  cross  line  is 
then  drawn  at  the  center.  In  cutting,  the  lens  must  be  placed  on 
the  machine  so  that  the  cross  line  comes  exactly  in  the  center 
of  the  pad,  otherwise  the  prism  power  will  be  reduced  or  in- 
creased. By  this  it  will  be  seen  that  a  sphero  prism  cannot  be 
treated  in  the  same  manner  as  a  piano  prism.  It  is  possible,  how- 
ever, to  twist  or  rotate  the  lens,  so  as  to  produce  a  prismatic  power 


Fig.  27 


Fig.  28 


in  the  opposite  direction,  and  double  prisms  can  be  obtained  by  the 
use  of  the  chart,  as  before  described. 

A  cylinder  prism  is  more  difficult  to  mark,  especially  if  the 
axis  is  oblique.  Also  when  the  base  of  prism  is  at  any  other 
point  than  at  vertical  or  horizontal.  For  example,  we  will  first 
select  the  simplest  form,  -|-  i  axis  90  ^  1°  in  or  out.    This  lens 


30 


The  Making  of  a  Mechanical  Optician 


will  have  no  power  in  the  vertical  meridian,  or  on  the  line  of  the 
axis.  There  also  should  be  no  prismatic  power  in  this  direction 
if  the  lens  is  ground  correctly.     If  there  is  a  prism  up  or  down, 


Dioptres 

«° 

H° 

y." 

|0 

2° 

0.50 

4.6 

.  , 

0  75 

3. 

1.00 

2.3 

4.6 

1.25 

1.8 

3.7 

55 

I  50 

1.5 

3.1 

4.5 

1.75 

1.3 

2.6 

3.9 

5.3 

200 

1.1 

2.3 

3.4 

4.6 

2.25 

1. 

2. 

3. 

4.1 

2.50 

.9 

1.8 

2.7 

3.7 

2.75 

.8 

1.7 

2.5 

3.4 

3.00 

.75 

1.5 

2.3 

3.1 

3.25 

.7 

1.4 

2.1 

2.8 

5.7 

3.50 

.65 

1.3 

1.9 

2.6 

5.3 

4.00 

.6 

1.15 

1.7 

2.3 

4.6 

4.50 

.5 

1. 

1.5 

2.1 

4.1 

5.00 

.45 

.9 

1.3 

1.8 

37 

5.50 

.4 

.8 

1.2 

1.7 

S.4 

6.00 

.35 

.7 

1.1 

1.5 

3.1 

Fig.  29 


the  lens  must  be  reground,  for  it  cannot  be  decentered  in  this 
meridian,  as  it  has  the  same  effect  as  a  piano  prism.  In  the  hori- 
zontal meridian  this  lens  has  a  power  of  +  i,  and  by  decentering 
the  prism  power  can  be  increased  or  decreased,  the  amount,  of 
course,  depending  on  the  size  of  the  lens  to  be  cut.  With  a 
.stronger  cylinder,  the  amount  could  be  considerable,  so  that  one 
can  readily  see  the  necessity  of  accuracy.  It  must  be  understood 
that  prism  power  and  decentration  are  the  same :  that  is,  by 
decentering  a  lens,  we  produce  prism  power.  Many  opticians 
seem  to  have  an  erroneous  idea  regarding  this  matter,  as  often  a 
customer  will  object  to  having  prisms  ground,  and  states  that  he 
wants  decentered  lenses.  If  a  prescription  is  ordered  with  the 
lenses  decentered  in  2  mm.,  perhaps  on  account  of  a  narrow  P.  D., 


The  Making  of  a  Mechanical  Optician 


31 


a  prism  is  produced  in  tlie  lenses,  although  the  original  idea  was 
to  obtain  the  correct  pupillary  distance.  If  this  were  thoroughly 
understood  by  every  optician,  it  would  make  the  work  much 
easier  for  the  prescription  houses. 

To  return  to  the  lens  in  question,  we  find  that  the  lens  must 
have  no  prism  power  in  the  vertical  meridian.  This  having  found 
to  be  correct,  we  proceed  to  dot  the  axis.  There  are  two  ways 
to  do  this — one  is  to  line  up  the  lens  at  right  angles  to  the  axis, 
and  the  other  is  to  place  the  test  prism  on  the  lens  to  be  marked 
and  dot  the  axis  just  as  if  there  were  no  prism  on  the  lens  at  all. 
By  the  first  method,  we  line  up  the  lens  so  that  the  line  is  contin- 
uous, and  place  a  dot  at  each  edge.  This  will  be  the  mechanical 
axis,  or  cutting  line.  This  line  can  then  be  drawn.  We  then 
select  a  1°  test  lens,  and  hold  it  over  the  lens  to  be  marked,  and 
center  the  lens  in  this  direction,  placing  a  short  cross  line  at  the 
point  where  the  lines  intersect.  By  this  it  will  be  seen  that  if  the 
prism  power  is  weak,  the  cross  line  will  be  moved  towards  the 
apex,  or  thin  edge,  and  if  strong,  towards  the  base,  or  thick  edge, 
which  shows  that  the  prism  was  not  accurately  ground.  It  also 
shows  us  that  a  lens  ground  with  a  1°  prism  could  be  decentered 


Fig.  30 


Fig.  31 


to  produce  •>4°  or  i/4°,  although  in  reality  the  lens  would  not 
be  large  enough  to  cut  an  ordinary  size  lens,  unless  the  focus  was 
strong  enough  {¥\g.  30). 

If  the  second  method  is  used,  the  test  prism  is  selected  and 
placed  over  the  lens  to  be  marked,  with  apex  to  base,  in  order  to 
neutralize  the  prism.  We  then  line  up  the  axis,  as  with  a  piano 
cylinder,  dotting  it  at  the  edges.     It  is  then  laid  on  a  card  with 


32 


The  Making  of  a  Mechanical  Optician 


cross  lines,  and  a  cutting  line  or  mechanical  axis  is  drawn  at  right 
angles  to  the  axis.  As  there  is  no  center  in  this  meridian,  it  does 
not  matter  where  this  line  is  drawn  as  long  as  the  size  of  eye 
can  be  cut  out  (Fig.  31). 

We  will  now  suppose  that  the  lens  was  +  i  axis  90  =  i  °  up 
or  down.    The  cylinder  would  have  no  power  in  the  vertical  meri- 


Fig.  32 


Fig.  33 


dian,  but  would  in  the  horizontal.  In  this  combination,  the  prism 
power  must  be  accurate,  as  there  is  no  possible  way  to  change  it 
by  decentration.  As  there  is  a  cylinder  power  in  the  opposite 
direction,  we  can  produce  a  prism  by  decentering  the  lens  in  or 
out  (Fig.  32),  so  that  if  care  is  not  used  we  will  get  a  double 
prism.  In  marking  a  lens  of  this  description,  either  of  the  two 
methods  before  described  can  be  used.  We  first  test  it  with  a 
prism,  to  ascertain  if  the  power  is  correct.  The  lens  will  then  be 
lined  up  on  the  axis,  in  the  same  manner  as  a  piano  cylinder.  If 
the  lens  has  been  ground  inaccurately,  so  there  is  a  little  prism 
base  in  or  out,  the  axis  dots  will  come  a  little  to  one  side.  This 
will  not  matter,  however,  as  long  as  the  size  required  can  be  cut 
(Fig.  33)- 

The  lens  is  then  placed  on  the  cross  lines,  and  the  cutting  line 
drawn  at  right  angles.  It  is  of  no  consequence  whether  this  line 
is  in  the  middle  of  the  lens  or  not,  as  far  as  the  prism  power  is 
concerned,  but  it  will  make  a  difference  in  the  thickness  of  the 
lens.    If  it  is  cut  near  the  base,  it  will  be  thick,  and  near  the  apex, 


The  Making  of  a  Mechanical  Optician  33 

thin.  If  the  lens,  when  surface-ground,  is  left  full  size,  it  can  be 
cut  fairly  near  the  apex,  as  it  will  be  quite  thick  enough  for  the 
frameless  lens.  A  prism  with  base  up  or  down  can  be  used  con- 
siderably thinner  than  one  in  or  out,  for  the  reason  that  in  the  first 
form  the  straps  are  fitted  in  midway  between  the  base  and  apex, 
whereas  in  the  second  form  one  strap,  if  a  spectacle,  must  be 
fitted  to  the  apex,  or  thin  edge,  and  if  an  eyeglass,  the  lens  can  also 
be  used  thin,  provided  the  base  is  in,  because  there  is  no  strap  to 
be  fitted  on  the  thin  edge,  except  possibly  a  handle,  and  nowadays 
these  are  rarely  used. 

If  the  lens  is  to  be  marked,  using  the  second  method,  test  the 
prism  power,  and  line  it  up  at  right  angles  to  the  axis,  placing  the 
dots  on  the  edge.  It  is  then  laid  on  the  card  and  the  mechanical 
axis  drawn.  We  then  hold  the  lens  in  the  hand,  and  sight  at  a 
line ;  by  moving  the  lens  until  the  line  is  continuous,  we  find  the 
center,  which  in  reality  is  the  axis.  In  both  these  methods, 
with  the  base  up  or  down,  it  must  be  remembered  that  the  prism 
power  must  be  ground  accurately,  and  tested  with  a  test  prism 
before  attempting  to  mark  it,  as  the  prism  power  cannot  be 
changed.  With  the  base  in  or  out.  the  prism  power  can  be  changed 
slightly  by  decentration,  as  described. 

Cylinder  prisms,  with  the  axes  oblique,  are  more  complicated ; 
consequently,  are  more  difficult  to  mark.  If  the  base  of  the  prism 
is  at  90°  or  180°,  the  prism  power  is  easily  neutralized,  and  the 
lens  is  then  marked  as  if  it  were  a  piano  cylinder.  If  the  prism 
power  is  accurately  ground,  it  simplifies  the  work  considerably, 
as  there  are  no  extra  conditions  to  deal  with.  There  are  many 
lenses  of  this  nature  in  use  to-day,  that  are  not  correctly  ground, 
and  yet  they  have  been  marked  and  cut  in  ignorance  of  the  fact 
that  there  is  prism  power  up  or  down  when  not  called  for  on  the 
prescription.  Every  optician  should  always  take  pride  in  the 
work  he  sends  out,  for  when  repairs  are  to  be  made  your  cus- 
tomer may  take  them  elsewhere,  and  as  your  case  bears  your 
name  your  reinitation  may  sufifer.  Oculists,  who  prescribe  many 
prisms,  usually  understand  them,  and  are  t|uite  particular ;  so  it 
pays  to  be  accurate  in  this  work.  A  very  easy  way  to  handle  this 
work  is  to  scratch  the  axis  on  the  rough  cylinder,  before  grinding 
the  prism,  but  this  is  very  apt  to  cause  breakage  when  heating  the 
glass  in  blocking.    If  there  is  only  an  occasional  lens  to  be  ground, 


34 


The  Making  of  a  Mechanical  Optician 


it  is  possibly  just  as  well  to  take  a  chance,  but  in  the  large  pre- 
scription shops  breakage  can  be  quite  an  item,  so  these  lenses  are 
usually  ground  without  scratching  the  axis. 


Fig.  34 

We  will  take,  for  example.  +  i  a-^is  45  =  i°  out,  and  sup- 
pose that  the  prism  is  accurately  ground — select  the  1°  test  prism 
and  place  it  over  the  lens  to  be  marked  with  the  ajiex  to  base. 
The  prism  is  then  neutralized,  and  the  lens  is  practically  a  piano 
cylinder.    Now  turn  both  lenses  so  the  axis  can  be  lined  up.  which 


^^.Vl^'lTT";, 


will  bring  them  cornerwise  (Fig.  34),  provided  the  cylinders  are 
ground  this  way.  After  dotting  the  edges  remove  the  test  lens, 
and  lay  the  lens  to  be  marked  on  the  axis  card,  with  the  dots  at 
45°.    Then  mark  the  cutting  line  or  mechanical  axis  in  fhe  middle 


The  Making  of  a  Mechanical  Optician  35 

of  the  glass,  but  without  a  cross  line  for  the  center  (Fig.  35). 
Now  take  the  test  prism  and  place  it  in  position  as  before,  and 
sight  at  a  straight  line.  This  will  appear  twisted,  as  in  Fig.  36, 
and  if  the  prism  power  is  correct,  the  line  will  be  cut  top  and 
bottom  an  equal  amount.  If  the  lens  is  not  held  in  the  correct 
position,  or  if  the  prism  is  not  correct,  it  will  be  cut  niore  at  one 
end  ^han  at  the  other  (Fig.  37).  By  moving  both  lenses  from 
side  to  side,  until  a  point  is  found  where  the  lines  break  evenly, 
a  center  will  be  found.  If  this  is  at  one  side  of  the  middle  of  the 
lens,  the  prism  power  is  strong  or  weak,  and  if  the  size  cannot 
be  cut,  it  must  be  reground  and  corrected. 

In  marking  cylinder  prisms  it  must  be  remembered  that  the 
lens  cannot  be  twisted,  but  must  be  cut  as  ground,  as  turning  the 


Fig.  36  Fig.  37 

lens  to  change  the  axis  turns  the  prism  also,  thus  making  a  double 
prism.  Turning  the  lens  to  make  the  prism  correct  will  bring  the 
axis  oflf  at  the  same  time. 

A  cylinder  prism  with  the  axis  oblique,  and  the  base  up  or 
down,  is  marked  in  the  same  way,  but  care  must  be  used  so  it  is 
not  decentered,  thus  producing  a  prism  in  or  out.  In  all  weak 
power  cylinders  the  decentration,  when  the  axis  is  oblique,  does 
not  amount  to  very  much,  and  possibly  will  do  no  harm  to  the 
wearer,  but  the  higher  powers  require  only  one  or  two  millimeters 
decentration,  to  produce  quite  a  little  prism  power.  With  the  base 
in  this  direction,  it  is  well  to  cut  it  as  near  the  apex  as  possible, 
and  if  the  center  comes  fairly  low  it  is  all  the  better  (Fig.  38). 

When  the  axis  of  the  cylinder  is  oblique,  and  also  the  base  of 


36 


The  Making  of  a  Mechanical  Optician 


prism,  it  really  produces  a  double  prism,  and  it  should  be  marked 
as  such,  unless  the  prism  is  at  the  same  axis  as  the  cylinder.  For 
example:  +  i  axis  45  =  2°  axis  45  would  be  either  -f  i  axis  45 


\V* 

\ 

// 

"^^ 

Fig.  38 


Fig.  39 


=  lYi"  out  =  i>4°  up,  or  +  I  axis  45  =  \]A°  in  =  ij^"  down 
in  the  left  eye.  If  this  combination  were  to  be  fitted  in  the  right 
eye,  it  would  be  -)-  i  axis  45  =  15^°  in  =  i>4°  up,  or  +  i  axis 
45  =  13^°  out  =  ii^°  down.  By  this  you  will  see  that  it  makes 
considerable  difference  to  which  eye  the  lens  is  to  be  fitted.  If  a 
lens  were  ground  for  the  right  eye  +  i  axis  45  =  iJ/^°  out  ^ 
ij^°  up,  it  could  be  fitted  base  in  and  down,  or  if  to  the  left  eye, 
it  would  be  in  and  up,  or  out  and  down.  These  points  must  be 
kept  in  mind  when  the  lens  is  being  ground,  also  when  marking, 
as  it  is  a  very  easy  matter  to  cut  them  wrong.  In  the  combination 
referred  to,  +  i  axis  45  =  2°  axis  45,  the  lens  would  first  be 
lined  up  on  the  a.xis  just  as  though  it  were  a  piano  cylinder,  and 
in  this  direction  the  lines  would  be  continuous ;  in  the  opposite 
direction  the  line  will  be  broken,  as  in  Fig.  39.  A  2°  test  lens 
should  then  be  held  over  the  lens  to  be  marked  with  the  apex  to 
base,  and  when  holding  the  two  lenses  with  the  axis  at  180°,  the 
lines  should  be  continuous  (Fig.  40).  If  the  lenses  are  held 
with  the  axis  at  45°,  the  lines  should  be  cut  evenly  at  the  top  and 
bottom  (Fig.  36).  Either  way  is  correct,  but  a  dot  must  be 
placed  in  the  center,  otherwise  the  power  of  the  prism  will  be 
changed.  When  the  three  dots  are  in  position,  that  is,  the  two 
at  the  outer  edges,  and  one  in  the  center,  the  lens  is  then  placed 
on  the  axis  chart  at  45°,  and  the  cutting  line  drawn. 

In  a  combination  with  the  base  of  prism  at  right  angles  to 


The  Makiiuj  of  a  Mechanical  Optician 


37 


the  axis,  for  example,  +  i  a^'s  45  =  2°  axis  145,  the  lens  is 
first  lined  up  across  the  axis,  as  at  this  point  the  line  will  be  con- 
tinuous, whereas  the  line  will  be  cut  on  the  axis.  This  condition 
is  just  the  reverse  of  Fig.  123. 

In  a  combination  with  the  axis  of  the  cylinder,  and  the  base 
of  prism  oblique,  but  at  different  axes,  the  marking  is  quite  diffi- 
cult. For  example:  -|-  i  axis  45  =  2°  axis  25.  In  this  case  we 
have  a  double  prism,  and  if  a  prism  chart  is  at  hand,  we  can  locate 
the  combination  very  easily  and  treat  the  lens  as  such.    This  com- 


Fig.  40 


Fig.  41 


bination  would  have  the  effect  of  about  i-)4°  in  =  1°  up  in  the 
right  eye,  and  would  appear  when  held  with  the  axis  at  45°,  as 
in  Fig.  41.  By  this  you  will  see  that  the  lines  are  cut  or  twisted 
in  both  meridians,  and  of  unequal  amounts.  With  the  proper 
test  prisms,  and  placed  in  the  correct  position,  the  lines  will  be  cut 
evenly.  In  a  complicated  lens  of  this  description  it  is  better  to 
mark  the  axis  of  the  lens,  or  the  cutting  line,  with  a  diamond 
before  surface-grinding,  and  in  this  way  it  is  only  necessary  to 
neutralize  the  prisms. 


CHAPTER  V 


MARKING    PRISMS — (Continued) 

Compound  prisms  are  dealt  with  in  much  the  same  manner 
as  cyhnder  prisms,  except  that  one  must  bear  in  mind  that  there 
is  power  in  both  meridians,  and  any  decentration  affects  the  power 
of  the  prism.  Any  combination  with  a  low  power  prism  will  have 
the  center  at  some  point  on  the  lens,  so  in  reality  it  is  really  a 
decentered  compound  (Fig.  42).  It  is  simply  necessary  to  place 
this   center   in    some    position    to   produce   the    necessary    prism 


Fig.  42 

effect.  This  is  the  theory  of  a  compound  prism,  and  the  only 
reason  any  desired  amount  of  prism  cannot  be  produced  is  that 
the  lens  is  not  large  enough.  If  one  will  keep  this  point  in  mind, 
the  handling  of  these  lenses  is  a  very  simple  matter. 

The  trouble  that  most  opticians  have  is  due  to  the  fact  that 
they  seem  to  have  an  idea  that  a  prism  is  some  mysterious  element. 
Take  for  example:  -(-  i  =  -j-  i  axis  90  =  1°  out.  This  is  one  of 
the  simplest  forms,  and  in  sighting  through  a  lens  of  this  com- 
bination we  find  that  it  is  centered  in  the  vertical  meridian,  and 
that  in  the  horizontal  meridian  the  center  is  at  one  side.  With  a 
-|-  2  spherical  we  find  by  referring  to  the  rule,  that  the  center 
is  five  millimeters  from  the  line  of  the  axis.  As  there  is  a  power 
of  2  D.  in  this  meridian,  we  would  by  decentration  of  5  mms. 
obtain  a  1°.  .As  this  is  more  than  the  size  of  the  lens  to  be  cut 
allows,  it  is  necessary  to  grind  the  prism — or  in  other  words,  we 


The  Making  of  a  Mechanical  Optician  39 

grind  a  lens  +1^+1  ^-^is  90,  but  with  the  center  five  milH- 
meters  to  one  side.  When  we  come  to  mark  the  lens,  if  the  full 
amount  of  prism  were  not  ground,  we  can  decenter  it  one  or  two 
millimeters  either  way,  to  produce  the  full  amount.  For  example : 
Suppose  the  lens  when  coming  from  the  surface  department  had 
the  center  y/2  millimeters  from  the  axis  line,  we  would  have  then 
but  about  }i°  prism;  by  decentering  the  lens  more  we  would  pro- 
duce the  1°.  If  the  lens  were  decentered  up  or  down,  we  would 
also  produce  a  prism  in  this  direction,  thereby  making  a  double 
prism.  With  a  cylinder  prism,  having  a  combination  of  -|-  i  axis 
90  ^  1°  out,  it  would  be  possible  to  cut  the  lens  at  any  point  in 
the  vertical  meridian  without  changing  the  power  in  any  way. 
This  is  explained  in  full  in  the  preceding  pages.  It  will  be  noted, 
however,  that  with  a  compound  prism,  it  is  impossible  to  do  this, 
and  that  the  lens  must  be  cut  at  one  point  on  the  vertical  meridian. 
If  the  lens  should  be  ground  with  a  slight  prism  up  or  down,  it 
could  be  decentered  to  cut  this  out. 

In  marking  this  combination,  first  line  it  up  at  right  angles 
to  the  axis,  place  a  dot  at  each  edge  of  the  lens,  and  this  will  be 
the  cutting  line,  or  mechanical  axis.  Then  select  a  1°  test  lens 
and  hold  it  over  the  lens  to  be  marked.  We  then  sight  at  a  straight 
line  and  bring  the  lens  in  center.  At  this  point  place  another  dot, 
and  this  will  be  the  mechanical  center ;  in  other  words,  this  point 
must  be  placed  in  the  center  of  the  pad  on  the  cutting  machine. 
If  a  pattern  is  to  be  used  to  cut  by  hand,  place  the  center  of  the 
pattern  on  this  point.  After  the  lens  is  cut,  it  will  be  seen  that 
this  is  not  the  true  center;  this  will  be  at  one  side.  If  we  are  not 
accurate  in  placing  the  lens  on  the  pad  or  pattern,  we  can  easily 
lose  some  of  the  prism  effect. 

A  sphero  cylinder  prism,  with  the  axis  at  90  or  180°,  com- 
bined with  the  prism  power,  base  up  or  down,  is  just  as  simple  to 
mark  as  a  combination  with  the  base  in  or  out.  For  example,  take 
-|-  I  ^  -(-  I  axis  90  ^  1°  lip.  This  will  have  the  effect  of  a 
compound  with  the  combination  -)-  i  =  -|-  i  axis  r;o,  but  the 
center  would  be  ten  millimeters  above  the  middle  of  the  lens.  In 
marking,  we  would  first  line  u])  tlie  lens,  finding  the  axis  just  as 
though  it  were  a  regular  comi>()und.  In  the  vertical  meridian  the 
line  would  be  continuous  ;  place  a  dot  at  each  edge  of  the  lens ; 
the  center  one  cannot  be  marked  at  this  time. 


40 


The  Making  of  a  Mechanical  Optician 


We  have  now  located  the  axis,  and  the  next  step  is  to  make 
the  cutting  Hne,  but  before  this  can  be  done  it  must  be  located 
with  a  prism.  Select  the  i°  test  prism,  and  place  it  next  the  lens 
to  be  marked,  and  line  it  up  at  right  angles  to  the  axis.     When 


f 

A 

\\ 

,'1 

\ 

/ 

^^^ 

-^ 

Fig.  43 

the  lens  is  in  position,  so  that  the  line  is  continuous  in  this  direc- 
tion, place  a  dot  at  this  point,  in  line  with  the  two  dots  marking 
the  axis.  Now  place  the  lens  on  the  axis  chart  and  draw  the 
cutting-  line.     A  short  cross  line  should  also  be  drawn  in  line 


Fig.   44 


with  the  axis  dots,  to  obtain  the  center  in  this  direction.  Fig.  43 
shows  the  position  of  line  in  opposite  direction  to  axis  before 
placing  prism  in  position. 


The  Making  of  a  Mechanical  Optician 


41 


A  sphere  cylinder  prism  with  base  up  or  down  can  be  de- 
centered  a  great  many  times  when  it  cannot  with  base  in  or  out, 
on  account  of  the  shape  of  the  lens.  It  is  very  rare  that  a  lens 
is  cut  wider  than  thirtv-five  millimeters,  and  most  of  theni  run 


only  from  thirty-one  to  thirty-three  millimeters.  As  the  rough 
lenses  are  forty-four  millimeters  from  corner  to  corner,  there  is 
quite  a  little  room  for  decentration  (Fig.  44).  It  should  always 
be  remembered  that  the  center  of  a  convex  lens  with  a  prism  will 
alwavs  be  towards  the  base,  and  that  the  center  of  a  concave  lens 


Fig.   46 

with  a  prism  will  be  towards  the  ape.x.     In  this  combination  just 
referred  to  the  center  will,  of  course,  be  up. 

\\'ith  a  combination  -|-   i  +  i  axis  45  =  2°  out,  the  hori- 
zontal line  will  be  cut  equally  (Fig.  451,  but  the  vertical  will  be 


42 


The  Making  of  a  Mechanical  Optician 


iiiiequal  (Fig.  46).  First  place  a  2°  test  prism  next  the  lens  to 
be  marked  to  neutralize  the  prism  power,  then  line  up  the  lens  on 
the  axis,  just  as  though  it  were  a  regular  compound  lens.  At  this 
time,  center  the  lens  in  the  opposite  direction,  also,  and  place  a 
dot  at  this  point.  Now  lay  the  lens  on  the  axis  chart  and  draw 
the  cutting  line.  After  marking  the  lens,  it  can  be  verified  by 
sighting  at  the  cross  lines :  these  will  appear  as  in  Fig.  46.  Now 
place  the  test  prism  in  place  again  and  it  will  be  noted  that  the 
lines  are  cut  equally  in  both  meridians. 

A  combination  of  -(-  i  ^  +  i  axis  45  ^  2°  axis  45°  will 
be  a  double  prism,  just  the  same  as  in  a  cylinder  prism,  and  should 
be  treated  as  such.    When  held  at  axis  45°  the  lines  will  appear 


Fig.   47 


Fig.   48 


cut  unequally  in  both  meridians  (Fig.  47).  By  turning  the  lens 
to  90°,  to  line  it  up,  it  will  be  noted  that  it  has  the  elYect  of  a 
regular  sphero  cylinder,  in  this  meridian;  therefore,  the  axis  is 
easily  lined  up.  After  placing  the  dots  on  both  edges,  take  the 
test  prism  and  place  it  next  the  lens  to  be  marked,  with  the  apex 
exactly  in  line  with  the  axis.  Now  sight  at  the  cross-line,  and 
move  the  lenses  until  the  vertical  line  is  cut  equally  at  top  and 
bottom  (Fig.  48).  Place  a  dot  at  this  point  and  we  have  the 
three  dots  in  position  to  mark  the  cutting  line.  Now  lay  the  lens 
on  the  axis  chart,  draw  the  cutting  line,  and  make  a  short  cross- 
line  for  the  center.  It  is  absolutely  necessary  to  mark  this  center, 
otherwise  the  power  of  the  prism  would  be  changed  if  the  lens 
were  cut  at  some  other  i)r)int  on  the  mechanical  axis. 


The  Making  of  a  Mechanical  Optician 


43 


A  combination  -f  i  =  +  i  axis  45  =  2°  axis  135  would 
appear  as  in  Fig.  47,  both  lines  being  cut  unequally.  When 
turned  to  axis  90,  as  in  the  previous  example,  it  will  not  line  up, 
but  the  lines  will  be  displaced  as  in  a  piano  prism  (Fig.  49).  In 
this  case  it  will  be  necessary  to  line  up  the  lens  at  right  angles  to 


Fig.  49 


the  axis.  In  this  direction  the  line  will  be  continuous.  Place  the 
dot  on  the  edges  in  the  regular  way  and  then  place  the  test  prism 
in  position  with  the  apex  at  135°.  Now  sight  at  the  vertical  line 
and  move  the  lenses  until  the  line  is  cut  equally  at  top  and  bottom, 
and  place  a  dot  at  this  point.  The  lens  is  then  laid  on  the  axis 
chart,  and  marked  as  before. 

With  a  combination  of  -|-  i  ^  +  i  a^'s  45  =^  2°  axis  25 
the  lines  will  be  cut  in  both  directions,  and  as  this  is  somewhat 
complicated  it  is  well  to  mark  the  axis  of  the  prism  with  a  dia- 
mond before  surface-grinding.  The  reason  for  this  is  the  diffi- 
culty to  place  the  test  prism  in  the  correct  position,  and  some 
guesswork  is  necessary.  This  combination  also  has  the  effect 
of  a  double  prism. 

In  grinding  all  combinations  of  double  prisms,  it  should  be 
remembered  that  the  correction  can  be  divided  between  the  two 


44  ^/'f  Making  of  a  Mechanical  Optician 

eyes,  and  still  have  the  same  effect.  For  example:  If  the  pre- 
scription calls  for  R.  +  I  =  +  I  axis  90  =  1°  up  and  1°  out, 
L.  +  I  =  -j-  I  axis  90  =  I  °  down  and  1  °  out,  we  could  grind  the 
lenses  R.  +  i  ^  +  i  axis  90  =  2°  up  and  L.  +  i  =:  -|-  i  axis 
90°  ^  2°  out.  This  simplifies  the  grinding  to  some  extent,  but 
the  disadvantage  is  that  we  do  not  produce  lenses  of  even  thick- 
ness. It  must  be  remembered,  however,  that  a  prism  base  out  in 
one  eye,  and  base  in  in  the  other  has  no  prismatic  effect,  as  one 
neutralizes  the  other.  This  also  applies  with  prisms  base  up  and 
down :  that  is,  two  lenses  placed  in  a  frame,  base  up,  have  no 
prismatic  effect,  and  when  dividing  the  prism  power,  one  must  be 
base  up  and  the  other  base  down.  We  rarely  see  mistakes  made 
with  prisms  in  or  out,  as  the  prescription  reads  the  same.  For 
example:  It  is  correct  to  write  a  prescription  -f-  i  ^  -)-  i  axis 
90  ^  I  °  out  OU,  and  in  this  case  the  prism  power  of  2°  is  equally 
dixided  between  the  two  eyes.  If  we  should  write  a  prescription 
-)-  I  =:  +  I  axis  90  =r  1°  up,  OU,  it  would  be  wrong,  as  both 
prisms  would  be  in  the  same  direction,  and  would  neutralize  each 
other.  The  correct  way  to  write  this  prescription  is:  Right  -|-  i 
=:  -(-  I  axis  90  =  1°  up  and  Left,  -|-  i  ^  i  axis  90  ^  1°  down. 
Test  prisms  for  neutralizing  should  always  be  marked  with 
a  diamond  on  the  ape.x  and  base,  also  at  right  angles  on  both 
sides.  When  the  lenses  are  marked  this  way  we  are  always  sure 
that  they  are  placed  in  position  correctly. 


MARKING  KRYPTOKS 

Some  opticians  prefer  to  purchase  their  Krx'ptok  lenses  un- 
cut, and  edge  them  in  their  nwn  shop.  In  marking  these  lenses, 
chalk  should  be  used  in  place  of  ink,  if  any  marks  are  to  be  placed 
on  the  disk.  For  this  purpose  a  glass  pencil,  such  as  is  used  for 
marking  china,  is  very  convenient.  It  is  blue  in  color,  and  is  very 
easily  distinguished  when  laid  on  the  axis  chart.  In  marking 
these  lenses,  the  first  step  is  to  make  a  series  of  dots  around  the 
edge  of  the  disk,  so  that  the  outline  can  be  distinguished  (  I-'ig. 
50).  We  next  line  up  the  distance  part  of  the  lens,  just  as 
though  it  were  an  ordinary  lens.  If  this  is  a  spherical,  we  need 
only  to  find  the  center  and  at  this  [joint  we  place  a  dot  or  ni;irk  a 
cross,  as  vou  jirefer.     W'c  now  lay  this  on  the  axis  chart,  with  the 


The  Making  of  a  Mechanical  Optician  45 

disk  in  the  center,  if  it  is  to  be  in  this  position,  and  draw  a  cutting 
line. 

For  lenses  of  this  character,  an  axis  chart  as  shown  in  Fig. 
31  is  a  great  convenience.  For  this  purpose,  take  an  ordinary 
paper  axis  chart,   and  at  a  point  eleven  millimeters  below  the 


Fig.   50 

center,  describe  a  circle  eighteen  millimeters  in  diameter.  This 
is  the  usual  size  of  the  disk  in  this  style  bifocal.  It  will  be  noted 
that  this  will  bring  the  top  of  the  circle  two  millimeters  below 
the  center  of  the  chart.  This  is  the  usual  position  of  the  disk  on 
all  lenses,  and  unless  otherwise  ordered,  a  disk  or  wafer,  if  a 
cement  bifocal,  should  be  placed  two  millimeters  below  the  center 
of  the  distance  lens.  It  is  always  well  to  consider  this  point,  how- 
ever, for  if  the  glasses  are  to  be  worn  constantly  and  the  patient 
desires  to  read  very  little,  a  small  disk  can  be  used.  On  the  other 
hand,  if  they  are  to  be  used  constantly  for  near  work  and  the 
patient  desires  only  to  glance  up  occasionally,  a  larger  disk  is 
more  desirable.  In  a  case  of  this  kind,  the  disk  is  brought  up  to 
the  center  of  the  distance  lens,  and  sometimes  above.  As  eighteen 
millimeters  is  the  average  size,  and  two  millimeters  below  center 
the  usual  position,  it  is  best  to  make  the  chart  this  way,  and  make 
the  necessary  allowances  for  the  occasional  conditions.  This  circle 
will  be  used  for  cases  where  the  disk  is  to  be  in  the  center,  and 
for  jobs  where  the  disk  is  to  be  set  in  one  or  two  millimeters 
it  is  necessary  to  have  another  circle. 


46 


The  Making  of  a  Mechanical  Optician 


For  this  one,  select  a  point  two  millimeters  at  one  side,  and 
in  the  same  line  as  the  first  one,  and  describe  another  circle  of 
the  same  size.  At  a  point  the  same  distance  on  the  opposite  side, 
describe  another  circle.  This  makes  three  circles,  one  in  the 
center,  and  one  at  each  side.  For  a  Right  lens,  we  will  use  the 
circle  at  the  left,  and  for  a  left  lens,  the  one  at  the  right.  These 
are  drawn,  however,  for  two  millimeters  displacement,  and  when 
it  is  desired  to  set  the  disk  in  but  one  millimeter,  the  disk  can  be 
placed  half-way  between  the  two. 

In  marking  a  spherical  lens  it  is  only  necessary  to  place  the 
center  of  the  distance  lens  on  the  center  of  the  chart,  and  twist 
the  lens  until  the  disk  coincides  with  the  circle  in  whatever  posi- 
tion you  desire  to  place  it.  A  cutting  line  or  mechanical  axis  is 
then  drawn,  and  the  lens  is  ready  to  cut.     In  cylinders  or  com- 


..  6Cr8S-90-9S-/00705. 


•*'-<'(i/.S6«6.SB-09-^'' 

Fig.   51 


pounds,  the  disk  is  dotted  as  before  described.  The  distance  lens 
is  then  lined  up  for  the  axis.  This  is  dotted  in  the  usual  way, 
but  always  select  the  meridian  that  does  not  pass  through  the  disk, 
if  possible.     For  example:  If  the  lens  is  to  be  axis  90°,  it  is 


The  Making  of  a  Mechanical  Optician  47 

better  to  line  it  up  on  the  180°  line  first,  as  we  can  then  sight 
away  across  the  lens.  If  we  line  it  up  at  90°  the  disk  interferes. 
When  the  a.xis  has  been  located  and  dotted,  lay  the  lens  on 
the  axis  chart,  with  the  dots  at  the  proper  axis,  and  'the  disk  over 
the  circle  which  is  in  the  correct  position.  It  will  be  noted  that 
this  lens  cannot  be  twisted  the  same  as  a  spherical.  In  twisting 
a  lens  of  this  kind,  either  the  axis  or  the  disk  will  be  thrown 
out  of  position.  We  can,  however,  move  the  lens  to  one  side  in 
order  to  bring  the  disk  in  the  correct  position,  without  changing 
the  axis.  In  laying  the  lens  on  the  chart,  notice  at  all  points  if 
the  lens  is  correct.  First  the  axis,  then  the  location  of  disk,  in 
or  out,  and  also  if  top  of  disk  is  the  correct  distance  below 
the  center  of  the  distance  lens.  If  all  points  are  correct,  draw  the 
cutting  line,  or  mechanical  axis.  If  for  any  reason  the  axis  is 
not  correct,  the  cylinder  can  be  reground  and  corrected,  provided 
the  lens  is  not  too  thin.  Also  notice  that  the  disks  on  the  two 
lenses  match  ;  that  is,  do  not  get  one  on  center,  and  one  set  in ; 
also  one  higher  than  the  other,  as  this  will  make  the  disks  appear 
different  in  shape  and  size  (Fig.  52).  Be  particular  also  when 
the  wafers  are  to  be  set  in  that  you  do  not  make  a  mistake,  and 
mark  both  lenses  for  one  eye.  If  this  shduld  happen,  you  will 
see  after  cutting  that  one  disk  will  be  in  and  the  other  out.  This 
will  necessitate  the  grinding  of  another  lens.  As  the  disks  on 
these  lenses  are  smaller  than  the  regular  cement  size,  and  also  as 
the  eyes  converge  looking  at  a  near  point,  according  to  theory, 
thev  should  alwavs  be  set  in  at  least  one  millimeter. 


MARKING  CROSS  CYLINDERS 

Cross  cylinders,  with  the  axes  at  right  angles,  are  just  as 
simple  to  mark  as  compounds,  but  with  the  axes  at  any  other 
angles,  it  is  very  difficult  to  find  the  correct  axis.  In  preparing 
lenses  of  this  character  to  be  surface-ground,  they  should  always 
be  scratched  with  a  diamond.  A  peculiar  feature  about  these 
lenses  prevents  their  being  lined  up  the  same  as  any  other  lens. 
This  is  the  fact  that  they  always  line  up  at  right  angles,  no 
matter  where  the  axes  are.  For  example :  +  i  axis  25  =  —  i 
axis  90  would  have  the  axes  according  to  the  prescription  65° 
apart,  and  yet  in  reality  they  would  line  up  at  90°  apart  just  the 


48  The  Making  of  a  Mechanical  0/^tician. 

same  as  any  compound.  The  true  position  of  tlie  lines  would  be 
at  axes  12°  and  102°  (Fig.  53).  If  we  could  transpose  a  com- 
bination of  this  kind  mathematically  in  a  few  seconds  we  would 
know  just  where  to  line  it  up.     As  this  is  impossible,  and  in  fact 


Fig.   52 

only  a  very  few  can  work  them  out  any  way,  it  is  much  better 
for  us  to  depend  on  our  axis  marks.  The  simplest  method  of 
transposing  cross  cylinders  is  to  take  two  cylinders,  and  after 
marking  the  axis  of  each,  place  them  together,  and  then  line  up 
the  combination.     If  one  finds  it  difficult  to  hold  them  without 


Fig.   53 

slipping,  the  two  plane  surfaces  can  be  cemented  together.  If  for 
any  reason  a  cylinder  is  surface-ground,  and  the  diamond  marks 
were  omitted,  the  simplest  way  to  locate  the  axis  is  with  the  lens 
measure.  First  locate  it  as  near  as  possible,  and  then  place  dots 
on  both  edges.     Then  take  the  lens  measure  again  and  place  the 


The  Making  of  a  Mechanical  Optician  49 

points  in  line  with  the  axis,  and  by  twisting  it  a  few  degrees  either 
way,  and  noticing  the  movement  of  the  pointer,  the  axis  can  be 
found  within  one  degree.  There  is  a  new  instrument  on  the 
market,  known  as  the  Axis  Indicator,  which  is  used  in  conjunc- 
tion with  the  lens  measure,  and  is  invaluable  for  this  work. 

BIFOCALS 

In  selecting  stock  for  bifocals  the  upper  lenses  are  marked 
as  usual  with  one  exception,  and  that  is,  the  wafers  are  always 
placed  on  the  inside  when  possible.  For  sphericals,  periscopic 
lenses  are  used  for  the  uppers  and  "regular"  wafers  are  cemented 
on  the  inside.  For  example:  Prescription  distance  +  2;  reading 
+  4,  select  -J-  2  Pcx.  and  a  "regular"  wafer,  having  a  +  2  power, 
which  is  the  necessary  addition  for  reading.  This  will  be  +  1.25 
on  one  side  and  -{-  .75  on  the  other.  The  +  1.25  side  is 
cemented  to  the  —  1.25  curve  on  the  upper  lens.  The  -|-  .75  on 
the  outside  of  the  wafer  and  the  +  3.25  on  the  outside  of  the 
upper  lens  will  then  give  us  the  required  focus  (Fig.  54).     The 


i-3.Z5r 


-*^ 


Fig.   54 

contact  surfaces  are  not  considered  in  any  way,  other  than  that 
they  must  fit  perfectly  as  they  have  nothing  whatever  to  do  with 
the  focus  of  the  lens  when  the  index  of  the  glass  is  the  same.  If 
it  is  different,  as  in  fused  bifocals,  it  is  then  an  important  matter, 
and  must  be  taken  into  consideration. 

For  cylinders  piano  wafers  are  used  and  cemented  on  the 
piano  side.  You  will  have  no  trouble  with  these,  as  the  power  of 
the  wafer  is  all  on  one  side.  Be  careful,  however,  never  to  cement 
a  wafer  on  a  cylinder  surface,  as  the  cylinder  effect  is  then  de- 
stroyed. Compounds  are  a  little  more  difficult,  but  are  simple 
when  understood.  The  wafer  is  usually  placed  on  the  inside  in 
weak  combinations.  The  only  reason  for  this  is  to  make  them 
more  invisible.    Whichever  way  they  are  made  the  wafer  will  have 


50 


The  Making  of  a  Mechanical  Optician 


to  be  cemented  to  the  spherical  surface,  and  here  is  where  you 
will,  perhaps,  be  confused  in  marking.  Be  sure  that  you  lay  the 
lens  on  the  protractor,  with  the  surface  upward,  that  is,  to  be  next 
the  eye.  If  the  spherical  is  to  be  in,  mark  it  on  the  spherical  side. 
Tf  the  cylinder  is  in,  mark  on  the  cylinder  side.  You  can  readily 
see  that  if  the  axis  is  to  be  45,  with  the  cylinder  surface  out,  and 
you  mark  it  on  the  cylinder  side,  and  then  turn  it  over,  the  axis 
will  be  135°.  In  selecting  the  wafers  the  contact  surface  will  be 
the  same  power  as  the  spherical  surface  on  the  compound,  but  the 
curve  will  be  the  reverse.  To  this  power  add  the  amount  to  be 
added  for  reading  and  you  will  have  the  outside  surface.  For 
example:  Prescription  +  i  3  +  -SO,  axis  90°,  distance  add  +  2 
for  reading.  We  will  first  select  —  i  to  fit  the  +  i  surface,  and 
by  adding  the  +  2  for  reading  we  have  +  3-  Then  the  wafer 
wanted  is  —  i  3  +  3- 

CUTTING 

You  should  first  become  familiar  with  the  working  of  your 
machine.  Read  the  directions  and  be  sure  that  you  understand 
how  to  set  it  for  size.    Some  of  them  are  set  by  charts.    That  is, 


Fig.  55 

for  length  and  width.  Others  are  set  by  the  difference  between 
the  length  and  width.  In  other  words,  the  patterns  are  marked 
from  4  to  12,  so  that  40  x  33  would  require  No.  7  pattern,  and  the 
gage  is  set  at  the  length,  40  mm.  In  cutting  for  frameless,  allow 
I  mm.  on  the  length  and  width.     For  above  size  it  should  be  cut 


The  Making  of  a  Mechanical  Optician 


51 


41  X  34.  For  frame  size,  it  is  best  to  cut  a  lens  and  try  it  in  the 
frame,  allowing  about  Y^  to  3/16  inches  between  the  end  piece, 
according  to  the  thickness.  After  you  have  ground  one  or  two, 
you  can  judge  for  yourself  just  the  amount  you  will  need  for 
grinding. 

When  the  machine  is  in  position  to  cut  the  handle  on  the  top 
gear  should  be  at  the  right.    It  should  always  be  turned  to  the  left, 


Fig.   56 

making  one  revolution,  and  stopping  at  just  the  point  where  it 
started  to  cut.  Never,  under  any  circumstances,  run  by  this  point, 
as  you  zmll  spoil  the  diamond.  If,  for  any  reason,  you  do  not  get 
a  satisfactory  cut  it  is  better  to  turn  it  over  and  try  again  on  the 
other  side.  In  placing  the  lens  on  the  pad  see  that  it  fits  perfectly 
flat  and  does  not  rock.  If  you  have  a  universal  pad  it  will 
be  all  right;  but  if  your  machine  has  a  number  of  pads  select 
the  one  nearest  the  curve  of  the  lens.  Also  cut  on  the  surface 
having  the  least  power  on  the  nearest  to  piano.  In  laying  the 
lens  on  the  pad,  the  cutting  line  should  be  on  the  180°  line  on 
the  cutter,  with  the  center  on  or  under  the  centering  pin,  which- 
ever way  the  machine  is  constructed.  When  the  lens  is  in  position, 
raise  it  to  the  diamond  by  pressing  the  hand  lever  on  the  left  side. 
Start  gently  at  first,  increasing  the  pressure  gradually,  turning  the 
lens  slowly  at  the  same  time.  Some  diamonds  require  more  pres- 
sure than  others,  but  you  must  experiment  carefully  until  you 
find  that  you  get  a  perfect  cut  (Fig.  55).  This  you  will  see  has 
a  sharp  line  which  runs  almost  through  the  lens.     If  you  put  too 


52  The  Making  of  a  Mechanical  Optician 

much  pressure  on  it  \(iu  will  have  a  scratch  (  Fig.  36  i.  This  lens 
you  will  find  very  difficult  to  break  down,  and  probably  break  over 
the  mark,  unless  you  are  extremely  careful. 

There  is  another  way  to  cut  a  lens  without  marking  and  in 
this  way  you  turn  the  pad  in  the  machine  so  that  the  line  corre- 
sponds to  whatever  axis  you  are  to  cut  on  the  graduated  scale. 
The  lens  is  then  placed  with  the  a.xis  dots  on  the  line  on  the  pad. 
This  will  give  you  the  same  result,  and,  although  it  saves  time,  it  is 
not  so  accurate.  Strong  lenses  and  high  curve  torics  can  be  cut 
better  by  hand.  These  are  marked  in  the  same  way,  selecting  a 
brass  pattern  the  exact  size  of  the  frame  or  the  dimensions  of 
the  frameless  lens  to  be  ground.  Lay  this  on  the  lens  with  the 
three  holes  over  the  dots,  or  on  the  cutting  line,  holding  it  in  the 
left  hand  with  your  thumb  on  the  pattern.  Use  the  diamond  in  the 
right  hand  in  a  vertical  position,  the  same  as  a  pencil,  or  with  the 
handle  between  the  index  and  third  fingers.  Cut  lightly  around 
the  pattern  and  be  careful  not  to  run  over  the  line. 


CHAPTER  VI 


CUTTING  COMPLICATED  LENSES 

Complicated  or  expensive  lenses  should  be  cut  by  hand  in 
some  cases,  and  although  many  are  cut  by  machine,  one  should  be 
sure  that  every  part  is  in  perfect  working  order.  One  of  the 
most  essential  things  is  to  see  that  the  pad  on  which  the  lens  is 
laid   fits  the  under  surface  of  the  lens  perfectly.      It   does  not 


Fig.   57 

matter  so  much  about  the  center,  unless  the  lens  is  very  thin  ;  in 
this  case  care  will  have  to  be  used  to  prevent  the  center  pin,  which 
keeps  the  lens  from  slipping,  from  punching  through  the  center. 
In  selecting  a  pad  to  fit  a  lens,  notice  if  it  has  a  good  bearing 
under  the  part  where  the  diamond  travels.    If  the  lens  has  a  deep 


Fig.   58 

curve,  and  the  pad  is  shallow,  the  point  of  contact  will  be  in  the 
center,  and  there  will  be  no  bearing  under  the  diamond.  In  a 
case  of  this  kind,  the  lens  has  a  tendency  to  rock  ;  this  is  not 
only  liable  to  cause  the  lens  to  slip,  but  even  if  the  diamond  cuts 
at  all,  the  best  results  will  not  be  obtained.  Fig.  57  shows  a  lens 
on  a  pad  too  deep ;  Fig.  58,  one  too  shallow ;  Fig.  59,  the  correct 
curvature.  These  illustrate  toric  lenses,  or  lenses  with  strong 
outside  curves. 

Flat  lenses  should  always  be  ])laced  on  a  flat  pad.     .Many 
opticians  neglect  to  change  their  pads,  however,  and  although  a 


54  The  Making  of  a  Mechanical  Of'tician 

flat  lens  could  be  cut  on  a  pad  liaving  a  slightly  concaved  surface, 
it  would  be  impossible  to  get  good  results  on  a  pad  having  a 
convex  surface,  as  the  lens  would  have  a  tendencv  to  tilt  (Fig. 
60). 


A  very  good  pad  is  now  furnished  with  some  machines,  that 
might  rightly  be  termed  "A  Universal  Pad."  This  consists  of  a 
flat  rubber  pad  having  a  raised  oval-shaped  center  (Fig.  61).     A 


Fig.   60 

flat  lens  when  lying  on  this  pad  will  rest  on  the  top,  and  as  the 
oval  is  about  the  average  size  of  lenses  cut,  it  has  a  very  good 
bearing.     A  convex  lens  rests  on  the  inside  of  the  oval,  and  as 


Fig.   61 

the  center  of  the  pad  is  cupped  out,  it  does  not  touch  at  this  point. 
A  concave  lens  rests  on  the  outside  of  the  oval,  and  as  the  pad 
is  flat  outside  of  the  raised  part,  it  allows  room  for  the  thick 


The  Making  of  a  Mechanical  Optician  55 

edges  to  overhang  (Fig.  62).    This  pad  can  also  be  used  for  toric 
lenses  of  ordinary  curve. 

Having  made  sure  that  the  lenses  rest  properly  on  the  pads, 
then  notice  if  the  foot  that  presses  in  the  center  is  adjusted  cor- 
rectly.    Some  machines  have  a  screw  adjustment  which  allows 


Fig.   62 

it  to  be  regulated  to  the  proper  tension,  and  others  work  entirely 
by  spring  tension.  The  points  of  contact  also  vary,  some  are 
just  a  rounded  metal  surface,  and  some  have  a  ring  about  %" 
diameter,  and  still  another  has  three  rubber-covered  points  in  the 
shape  of  a  tripod.  Whatever  style  is  used,  be  sure  that  they  are 
adjusted  to  prevent  the  lens  from  changing  its  position,  thereby 
throwing  the  axis  out ;  or  else  obtaining  an  irregular  shape.  Next 
be  sure  the  diamond  is  cutting  in  good  shape;  do  not  attempt  to 


Fig.  63 

use  one  that  needs  resetting,  as  a  poor  diamond  can  easily  spoil 
a  pair  of  lenses  that  would  cost  more  than  the  cost  of  resetting. 

That  the  formation  of  a  cutting  stone  may  be  thoroughly 
understood,  we  show  an  enlarged  illustration  of  a  point  (Fig.  63). 
This  is  of  natural  formation,  and  cannot  be  recut.  It  can  be 
reset  at  a  different  angle,  or  if  this  point  has  been  damaged,  a 
new  one  on  the  same  stone  can  be  used.  The  best  machines  are 
supplied  with  Brazilian  sparks,  and  although  African  sparks  look 
the  same  to  a  novice,  they  will  not  produce  as  good  results.  This 
point  should  always  be  considered  when  purchasing  a  machine. 
This  also  applies  to  hand  diamonds.  Many  opticians  have  a 
mistaken  idea  regarding  these  tools.    There  are  offered  for  sale 


5^^ 


The  Making  of  a  Mechanical  Optician 


glazer's  diamonds  at  a  low  figure,  and  many  times  they  are 
purchased  at  pawnshops  or  second-hand  stores  as  low  as  one 
dollar.  A  good  hand  diamond  for  optical  use  costs  at  least  five 
dollars,  and  is  well  worth  the  investment  (Fig.  64). 


c 


XI> 


Fig.    64 

A  diamond  that  has  lost  its  cutting  point  will  only  scratch. 
As  soon  as  this  is  noticed,  experiment  a  little  and  see  if  a  cut 
cannot  be  obtained  by  using  a  different  pressure.  The  amount 
of  pressure  required  varies,  but  this  does  not  necessarily  mean 
that  the  best  diamonds  require  light  pressure.  In  fact,  one  that 
requires  a  fairly  firm  pressure  is  to  be  desired,  as  a  cut  may  then 
be  forced  away  through  the  glass.    As  previously  stated,  as  soon 


Fig.   65 

as  it  is  noticed  that  the  diamond  is  ntjt  cutting  properly,  have  it 
attended  to  at  once. 

There  is  another  point  regarding  the  setting  of  a  diamond, 
and  that  is  the  angle.  A  diamond  may  cut  properly  in  a  straight 
line,  but  when  used  on  curves  it  will  not  cut  at  all.  We  occa- 
sionally find  this  trouble  with  cutting  machines,  and  frequently 
the  lens  may  be  cut  all  right  all  the  way  around,  except  at  one 
point  on  the  side  (Fig.  65  I.  At  this  point  the  diamond  has  a 
tendency   to   travel   away   from   the   pattern,   thereby   causing  a 


The  Making  of  a  Mechanical  Optician 


57 


hump  on  the  side.  This  may  be  prevented  in  some  cases  by 
increasing  the  spring  tension,  but  if  it  requires  more  than  a  rea- 
sonable amount,  or  if  it  does  not  remedy  the  difficulty,  the  dia- 
mond should  be  reset. 

There  may  be  another  cause  for  this,  and  that  is  the  microm- 
eter head  may  not  swing  easily  in  the  arm  that  holds  it.    In  most 


Fig.   66 


machines  tliere  is  a  set  screw  with  a  check-nut  at  the  top  to 
regelate  the  play  at  this  [joint.  This  should  be  adjusted  so  there 
is  no  play  up  and  down,  but  so  the  micrometer  head  swings  easily. 
A  drop  of  oil  at  this  point  will  also  help  a  little.  If  this  is  adjusted 
so  that  it  works  too  stiflf,  the  micrometer  head  has  a  tendency 
to  travel  in  a  straight  line,  rather  than  to  follow  the  curve  of 
the  pattern. 

This  theory  also  applies  to  a  hand  diamond,  and  we  find  in 
use  a  great  many  so-called  pencil  diamonds.  These  are  simpiv 
straight  handles  with  a  diamond  set  in  the  end.  They  may  pos- 
sibly have  one  cutting  point,  but  as  a  rule  are  intended  for  scratch- 
ing, marking  or  writing  on  glass.  .A  good  hand  diamond  has  a 
swivel  in  which  the  diamond  is  set.  and  in  this  way  the  point 
follows  the  curve  of  the  pattern.  The  best  glazier's  diamonds 
are  also  made  in  this  way.  but  the  swivel  is  verv  large,  and  is 
intended  to  be  used  with  a  thick  straight  edge.  An  optician 
uses  a  diamond  around  a  thin  brass  pattern,  consequently  these 
will  not  answer.  The  regular  optician's  diamond  is  set  so  that 
one  side  of  the  stone  bears  directly  against  the  pattern,  and  in 
this  way  a  close  cut  is  obtained.  Rather  than  use  a  poor  diamond, 
one  can  just  as  w^ell  use  a  steel  point.  One  of  the.se  can  be  made 
\ery  easily  mit  of  a  rat-tail  file,  ;uul  by  grinding  ;i  slinrt  stubbv 


58  The  Making  of  a  Mechanical  Optician 

point  it  will  scratch  as  well  as  a  diamond.  Many  use  these  for 
cutting  (although  really  scratching)  wafers.  If  one  desires  good 
cutting,  it  can  only  be  obtained  with  the  best  diamonds. 

After  a  diamond  has  been  reset,  it  will  be  necessary  to  change 
the  size  adjustment.  Some  machines  are  so  arranged  that  this 
can  easily  be  done,  and  others  require  special  scales ;  in  either 
case,  cut  a  lens  and  measure  it  with  a  rule.  Then  work  from 
this  as  a  basis,  and  if  you  are  obliged  to  make  out  a  chart,  do 
so;  but  if  the  machine  can  be  adjusted,  it  is  much  more  satis- 
factory. 

For  breaking  down  lenses  after  they  are  cut,  breaking  tongs, 
similar  to  Fig.  66,  are  to  be  preferred.  Many  use  flat  nose,  or 
cutting  pliers.  There  are  also  tongs  with  straight  jaws,  but  those 
with  the  side  jaw  are  easiest  to  handle.  These  jaws  on  the  inside 
are  rough,  so  that  they  grip  the  glass  in  good  shape ;  other 
pliers,  such  as  cutting  pliers,  snap  the  glass  rather  than  break  it 
easily. 

In  breaking  down  lenses,  hold  the  lens  in  the  left  hand, 
using  the  side  of  the  breaking  tongs,  and  start  on  the  end  of  the 
lens.  Do  not  use  the  top,  as  this  is  somewhat  awkward.  After 
breaking  it  down  as  well  as  possible,  cribbers  should  be  used 
(  Fig.  6/ ).    These  consist  of  a  pair  of  scissors,  so  to  speak,  having 


Fig.   67 

square  iron  pieces  on  the  inside  of  the  jaws.  The  glass  will 
roughen  the  iron,  and  gradually  wear  it  away,  and  at  the  same 
time  it  makes  a  natural  shape  which  seems  to  take  hold  of  the 
glass  better.  A  workman  using  these  all  the  time  will  wear  them 
down  to  a  point  where  they  can  hardly  be  used,  rather  than  fit 
new  pieces  to  the  jaws  in  order  to  preserve  the  curve  in  the  jaws. 
After  the  jaws  have  been  worn  consi(leral)ly,  they  can  be  turned 


The  Making  of  a  Mechanical  Optician  59 

over,  and  the  opposite  side  used.  These  pieces  are  soft-soldered 
to  the  jaws,  and  need  only  to  be  heated  slightly,  and  will  then 
drop  off.  The  end,  it  will  be  noticed,  is  fitted  with  a  screw ;  this 
is  to  allow  for  different  thicknesses  of  lenses. 

Strong  concave  lenses,  thick  prisms  and  deep  torics  can  best 
be  cut  by  hand,  and  for  this  purpose  the  thin  brass  patterns  are 
used.  These  can  be  curved  to  fit  the  surface  to  be  cut.  If  one 
does  not  have  an  automatic  machine,  the  lenses  must  be  cut  and 


Fig.   68 

shaped  better.  With  an  automatic  grinder  many  of  these  thick 
lenses  can  be  cut  large,  and  the  machine  can  be  set  to  grind  to 
size.  This  method  is  used  by  some  opticians  for  frame  work. 
The  bevel  is  then  put  on  afterward  by  hand. 

Automobile  goggles  require  a  great  many  shapes,  and  if  one 
does  not  have  an  assortment  of  metal  patterns,  a  temporary  one 
can  be  cut  out  of  cardboard.  Many  of  these  lenses  are  made 
from  window  glass,  or  in  other  words,  it  is  blown  instead  of 
moulded.  Glasses  for  stone-cutter's  spectacles  are  also  made 
from  this  quality  of  glass,  and  if  one  has  much  of  this  class  of 
work  to  do,  it  is  better  to  have  a  special  diamond  for  the  purpose, 
especially  for  machine  work.  This  point  should  also  be  kept  in 
mind  when  ordering  a  diamond  reset,  for  it  is  possible  to  reset  a 
diamond  that  will  cut  perfectly  on  one  kind  of  glass,  and  give 
very  satisfactory  results  on  another.  This  also  applies  to  B.  &  L. 
and  A.  O.  Co.  glass.  If  a  diamond  is  set  for  B.  &  L.  it  may  not 
produce  good  results  on, A.  O.  Co.,  although  we  have  always 
found  that  one  set  for  A.  O.  Co.  will  cut  B.  &  L.  If  your 
diamond  is  to  be  reset  by  any  other  than  an  optical  workman,  it 
is  a  good  idea  to  furnish  them  with  samples  of  both  kinds  of 
glass,  otherwise  they  will  ])robahly  use  window  glass  to  e.xperi- 


6o 


The  Making  of  a  Mcclianical  Of'tician 


ment  on,  and  the  best  results  will  not  be  obtained  on  optical  glass. 
No  matter  what  method  or  what  machine  you  use,  it  is  well  to 
watch  an  expert,  if  possible,  or  at  least  see  samples  of  what 
can  be  done  by  others.  In  this  way  you  can  readily  see  if  you 
are  getting  all  that  you  can  out  of  your  machine.  If  you  do  not, 
there  is  trouble  somewhere,  either  with  vou  or  with  the  machine. 


Fig.   69 

There  are  many  odd-shaped  lenses  in  use  at  the  present 
time,  but  the  majority  can  be  cut  by  machine.  Many  opticians 
do  not  understand  that  drop  eyes  (Fig.  68)  can  be  made  with 
any  difference  between  the  length  and  width.  Although  Xo.  9 
is  the  regular  shape  for  an  oval  lens,  in  the  drop  eye  it  looks 
somewhat  pointed.  Xo.  7  shape  (Fig.  70)  is  to  be  preferred  to 
No.  9,  and  if  one  desires  still  more  drop.  Xo.  5  makes  a  good 
shape.    These  patterns  are  carried  in  stock  by  the  factories,  with 


proportions  ranging  from  4  to  10,  and  if  it  is  possible  to  use 
them  on  your  machine,  it  will  save  considerable  work,  as  well  as 
time,  to  have  them. 

Clerical  eyes  cannot  be  cut  by  machine  on  account  of  the 
flat  top,  and  also  because  usually  the  width  is  very  narrow.    The 


The  Making  of  a  Mechanical  Optician  6i 

most  common  sizes  are  40  x  20  and  38  x  18.  These  are  also  made 
with  a  crescent-shaped  top.  All  these  styles  have  to  be  cut  by 
hand. 

There  are  also  many  lenses  in  use  that  have  what  is  com- 
monly called  "full  ends"  (Fig.  69).  These  run  slightly  more 
toward  a  square  shape  than  the  regular  ovals.  Patterns  for  your 
machine  can  also  be  obtained  for  this  class  of  work,  although  if 
your  machine  has  a  fi.xed  pattern  that  cannot  be  changed,  these 
can  be  cut  by  hand.  A  great  many  opticians  are  running  on 
special  shapes  of  this  kind,  on  account  of  the  advertising  feature, 
as  well  as  the  desire  to  be  exclusive.  In  a  small  city  or  town 
having  four  or  five  opticians,  competition  is  very  apt  to  be  keen. 
If  one  of  these  grinds  a  special  shape  it  may  be  possible  that 
his  competitors  may  not  have  grinding  plants,  and  in  this  case 
they  are  unable  to  use  a  stock  lens,  but  will  be  obliged  to  send 
it  away.  As  this  will  take  at  least  twenty-four  hours,  the  cus- 
tomer may  object  to  waiting  that  length  of  time.  The  original 
maker  could,  however,  duplicate  the  lens  while  the  customer 
waited,  if  necessary,  and  in  this  way  it  forces  the  customers  to 
bring  their  repairs  to  him.  If  you  desire  to  have  a  shape  of  your 
own,  it  is  well  to  have  a  special  pattern  made  for  this  purpose. 


CHAPTER  VII 


LENS  GRINDING 

For  hand  grinding  a  large  stone  is  preferable,  and  the  size 
most  commonly  used  is  24  inches  diameter  hy  lyi  inches  face. 
Craigleith,  corundum  or  carborundum  can  be  used,  but  the  corun- 
dum, called  by  the  trade  name  Alundum,  is  the  best.  This  size 
should  run  at  about  225  revolutions,  or  141 5  feet  per  minute.  To 
obtain  the  proper  speed  for  any  size  stone,  multiply  the  diameter 
^y  3  i/7>  ^"d  then  multiply  by  the  number  of  revolutions 
desired. 

The  stone  should  turn  away  from  the  grinder  and  should  be 
kept  wet  by  a  drip  or  sponge  on  the  back.  It  is  unnecessary  to 
have  a  great  amount  of  water  on  the  stone,  so  that  it  will  fly  all 
over  everything,  but  keep  it  just  wet  enough  so  that  it  will  not  run 
dry.  With  ordinary  care  the  stone  will  keep  in  shape,  but  if  it 
becomes  rough  it  should  be  smoothed  with  a  piece  of  the  same 
material.  Do  not  use  a  piece  of  craigleith  on  an  alundum,  or 
vice  versa. 

The  turning  can  be  done  by  hand,  but  not  as  well.  When 
turning  without  a  truing  device  the  diamond  is  held  in  tlie  right 
hand  and  the  left  is  used  to  steady  and  guide  it.  A  board  is 
placed  on  the  trough  at  the  back,  so  that  it  just  clears  the  stone; 
this  is  used  as  a  rest.  The  diamond  tool  is  then  started  at  either 
edge  and  rolled  along,  so  to  speak,  on  the  rest,  so  that  the  stone  is 
cut  evenly.  Enough  should  be  taken  off  so  that  the  surface  is 
square  and  true.  A  carbonmdum  block  should  then  be  used  on 
the  back  to  smooth  it,  or,  in  other  words,  take  out  the  ridges  left 
by  the  diamond.  The  stone  should  then  be  honed  with  a  piece  of 
the  same  material,  held  in  the  hands,  on  the  front. 

When  the  lenses  are  cut  and  ready  to  be  ground,  they  should 
be  rinsed  in  water  to  remove  all  the  glass  dust,  otherwise  this  gets 
into  the  fingers,  and  as  the  lens  is  revolved,  it  scratches  the  sur- 
face. In  large  shops  there  is  apt  to  be  quite  a  little  waste  from 
scratching,  and  this  is  usually  the  cause.  A  rubber  coin  pad,  such 
as  are  often  seen  on  counters,  and  which  can  be  obtained  in  any 


The  Making  of  a  Mechanical  Optician  63 

rubber    store,    is    convenient    to    lay    lenses    on,    and    prevents 
scratching. 

If  the  lenses  are  well  shaped  with  the  cribbers,  there  is  very 
little  difficulty  in  putting  on  the  level,  but  if  there  are  bunches  and 
points  to  be  ground  off,  this  is  where  skill  is  required.  The 
shaping  is  the  first  important  point,  and  the  eye  should  be  trained 
to  judge  ovals.    The  axis  should  also  be  watched  at  the  same  time 


Fig.   71 

and  see  that  you  do  not  grind  it  off.  If  the  lens  is  cut  large,  and 
this  very  often  happens,  it  is  a  good  plan  to  mark  it  occasionally. 

In  shaping  the  lens,  it  should  be  held  between  the  thumb  and 
forefinger  of  both  hands  (Fig.  71)  at  a  slight  angle,  turning  it 
from  left  to  right.  The  points  and  bunches  should  be  taken  off 
until  you  have  a  good  oval.  The  lens  should  then  be  held  between 
the  thumb  of  the  right  hand  and  the  forefinger  of  the  left 
(Fig.  72).  It  should  then  be  revolved  with  the  forefinger  of  the 
right  hand  as  far  as  possible  and  then  picked  up  with  the  thumb 
of  the  left  until  you  can  get  another  hold  with  the  forefinger  of 
the  right  hand.  In  this  way  the  lens  can  be  revolved  as  steadily 
as  if  it  were  in  a  machine.  If  you  have  trouble  with  the  lens  stick- 
ing to  your  fingers,  a  little  piece  of  soap  can  be  kept  handy,  and 
by  just  touching  it  occasionally  you  will  avoid  this  annoyance. 

The  lens  should  be  beveled  a  little  first  on  one  side,  then 
turned  over  and  ground  the  same  amount  on  the  other.  Too  much 
pressure  should  not  be  used,  as  it  is  better  not  to  try  to  grind  too 
fast.  As  soon  as  the  lens  is  beveled  on  both  sides,  it  should  be 
tried  in  the  frame  for  size.    The  screw  should  be  taken  out  and 


64 


The  Making  of  a  Mechanical  Optician 


the  temple  removed,  and  to  bring  the  joints  together,  an  old  pair 
of  cutting  pliers  having  the  edges  drilled  should  be  used. 

As  the  lens  is  tried  in  the  frame,  you  should  learn  to  judge 
the  amount  it  .will  be  necessary  to  grind  off.  In  any  case,  how- 
ever, the  lens  should  be  tried  frequently,  so  that  it  will  not  be 
ground  too  small.  It  should  be  fitted  so  that  the  joints  just  come 
together,  and  no  light  can  be  seen  between  them  with  the  lens 


Fig.   72 


perfectly  tight,  and  as  the  joints  are  held  with  the  pliers  in  the 
right  hand,  try  to  twist  the  lens  with  the  left.  The  level  should  be 
perfectly  smooth,  and  equal  on  both  sides,  with  no  chips  or  bright 
places;  if  it  does  not  come  out  this  way  the  lens  was  cut  too  small. 
Just  before  trying  the  last  time,  the  lens  should  be  held  in  the 
right  hand  between  the  thumb  and  forefinger  in  a  vertical  position, 
and  allowed  to  turn  on  the  stone  a  couple  of  times  to  take  off  the 
sharp  edge,  otherwise  it  will  chip  when  the  joints  are  screwed  up. 
When  the  lens  is  placed  in  the  frame  see  that  the  strongest 
concave,  or  weakest  convex  surface,  is  next  the  eye,  so  that  the 
axis  will  be  right  (the  lens  should  have  been  cut  this  way).    Also 


The  Making  of  a  Mechanical  Of'fician  65 

see  that  the  ends  of  the  lens  come  to  the  center  of  the  joints  and 
foot  of  the  bridge.  Never  mind  if  the  frame  is  out  of  shape,  put 
the  lens  in  right  and  true  the  frame  so  that  the  lenses  will  be  hori- 
zontal afterward.  In  grinding  the  lens  for  the  other  eye  care 
should  be  used  to  keep  the  shape  the  same. 

When  grinding  torics,  coquilles  and  strong  lenses,  the  frame 
should  be  curved  slightly  to  conform  with  the  shape  of  the  lens, 
otherwise  the  eye  wire  will  spring  off  the  bevel,  causing  the  lens 
to  drop  out.  Clerical,  or  half  eyes,  are  difficult  to  grind  and  care 
should  be  used  to  fit  the  corners  well  before  attempting  to  reduce 
the  lens  to  size.  After  the  corners  and  top  are  fitted  the  surplus 
glass  can  be  ground  off  the  lower  part. 

Pebbles  cannot  be  ground  successfully  on  an  ordinary  alun- 
dum  stone,  as  special  grit  is  required.  Carborundum  is  the  best, 
but  craigleith  answers  the  purpose  very  well,  although  it  is  slow 
cutting. 

Window  glass  should  not  be  ground  on  your  stone,  as  this  has 
a  tendency  to  rough  it. 

Strong  lenses  require  a  steeper  bevel  than  the  regular,  and  as 
the  high  power  convex  are  thin  on  the  ends  and  thick  on  the  sides, 
it  is  well  to  start  the  bevel  on  the  sides  first  and  grind  the  ends 
last,  otherwise  the  lens  will  be  too  full. 

In  fitting  lenses  to  rubber  or  zylonite  frames,  the  frames 
should  be  softened  in  hot  water  or  over  a  gas  flame.  Extreme 
care  must  be  used  not  to  burn  the  frame.  Shell  should  never  be 
attempted,  as  these  are  very  brittle  and  are  costly  to  repair.  When 
fitting  lenses  to  metal  lorgnettes,  it  is  advisable  to  cover  the  handle 
with  tissue  paper  or  cloth  to  prevent  scratching.  We  advise, 
however,  that  these  difficult  jobs  be  sent  to  the  prescription  houses, 
as  it  is  often  expensive  to  repair  or  replace  these  frames  should 
they  become  damaged  or  broken. 

For  hand  grinding  the  lens  is  cut  yi  mm.  larger  all  around, 
and  the  first  operation  is  to  shape  it.  It  is  held  in  the  center 
between  the  thumb  and  forefinger  of  the  right  hand  in  a  vertical 
position.  The  left  thumb  and  forefinger  are  used  as  a  rest  and 
guide  (Fig.  73).  The  points  and  bunches  are  then  ground  off 
until  you  have  a  true  oval.  The  lens  is  then  held  in  the  same 
position,  but  allowed  to  revolve  slowly.  This  is  done  by  pressing 
gently  against  the  stone  and  allowing  the  lens  to  slip  between  the 
fingers  in  the  right  hand ;  the  left  is  simply  to  steady  and  guide  it. 


66 


The  Mahiiig  of  a  Mechanical  Optician 


Care  should  be  taken  not  to  let  it  get  away  from  you,  but  with  a 
little  practice  it  can  be  revolved  as  steadily  as  a  machine. 

After  the  lens  is  down  to  size  and  the  edge  is  flat  and  smooth, 
the  sharp  edge  should  be  taken  off,  or,  in  other  words,  put  on  a 
very  small   bevel.     Strong  lenses   and   torics  will   require   more 


Fig.   73 

bevel  where  the  straps  are  fitted  to  prevent  chipping.  In  this 
operation  the  lens  is  held  in  the  same  position  as  in  grinding 
lenses  for  frame  (Fig.  /2).  If  a  new  pair  of  lenses  is  being 
ground  they  should  be  measured  in  millimeters  for  length  and 
width.  The  sizes  are  as  follows:  i  eye,  37  x  28;  o  eye,  38J^4  x 
29J^  ;  00  eye,  40  x  31 ;  000  eye,  41  x  32 ;  0000  eye,  44  x  30.  Full 
eyes  or  short  ovals  are  the  same  length,  but  two  (2)  mm.  wider. 

For  measuring,  a  millimeter  rule  is  considered  accurate 
enough,  but  if  you  wish  to  be  exact,  a  Boley  gage  is  better.  In 
matching  a  broken  lens,  you  can  lay  the  new  one  over  tlie  old  one 
and  judge  the  size,  but  this  requires  practice.  The  shape  should 
also  be  noted  as  it  is  possible  to  grind  two  lenses  having  the  same 
length  and  width,  but  the  shape  will  be  different,  one  may  have 


The  Making  of  a  Mechanical  Of'tician  67 

full  corners  (Fig.  74)  and  the  other  pointed  (Fig.  75).  Some 
prefer  the  shape  with  full  corners,  as  it  gives  a  straighter  surface 
for  the  strap  to  bear  against,  and,  consequently,  does  not  loosen 
as  easily. 

Drop  eye  lenses  (designated  by  various  trade  names  in  differ- 
ent parts  of  the  country)  are  ground  in  the  same  manner.    These 


Fig.   74  Fig.   75 

are  ground  off  axis  very  easily,  so  this  point  should  be  looked  out 
for.  Also  see  that  the  ends  are  not  ground  too  quickly,  as  the 
shape  will  lose  its  identity  and  the  results  will  be  more  like  a 
regular  oval. 

DIFFERENT  METHODS  OF  GRINDING 

\\'e  have  already  described  the  correct  methods  of  grinding, 
but  as  there  are  other  methods  in  common  use,  we  will  add  a 
few  suggestions.  ]!y  correct  methods  is  meant  those  that  are 
most  generally  used  by  expert  workmen,  and  are  usually  adopted 
by  the  most  successful.  There  are  many  grinders  that  prefer 
their  own  method,  and  some  of  these  may  come  easier  to  certain 
individuals. 

The  first  method  adopted  by  the  beginner  for  hand-grinding 
is  that  described  and  illustrated  on  page  64  (Fig.  y^i^.  While 
this  is  supposed  to  be  used  only  in  shaping  the  lens,  many  op- 
ticians continue  to  grind  the  entire  bevel  in  this  manner.  A  very 
fair  job  can  be  obtained  by  this  method,  but  the  edge  will  always 
show  little  points  or  humps  where  the  position  was  changed  in 
order  to  obtain  a  new  hold  on  the  lens.  For  factory  work,  and 
also  prescription  work,  as  it  is  turned  out  by  the  best  prescription 
houses,  this  would  hardly  answer,  as  the  bevel  must  be  continuous 
and  regular  in  order  to  pass  inspection. 


68  The  Making  of  a  Mechanical  Of^tician 

The  correct  and  most  common  method  is  shown  in  Fig.  74, 
page  65,  but  another  that  is  equally  as  good  is  one  where 
the  lens  is  held  in  the  right  hand  between  the  thumb  and  fore- 
finger. This  position  as  far  as  holding  the  lens,  is  the  same  a.=: 
in  Fig.  75  (which  is  the  correct  position  for  rimless  grinding), 
illustrated  on  page  65  of  this  chapter.  Instead  of  holding  it  in  a 
vertical  position  as  in  grinding  rimless  lenses,  it  is  held  on  the 
stone  at  an  angle  of  135°.  If  the  lens  were  held  in  a  vertical 
position,  and  then  tipped  to  one  side  in  order  to  obtain  the  correct 
angle  for  the  bevel,  the  forefinger  would  naturally  touch  the  stone. 
By  turning  the  lens  at  an  angle  of  135°,  a  convenient  position  is 
found,  and  at  the  same  time  the  correct  angle  for  the  bevel  is 
obtained.  By  a  little  experimenting,  one  can  find  an  angle  to  suit. 
When  this  angle  has  been  located,  allow  the  lens  to  bear  on  the 
stone,  and  it  will  be  noted  that  as  the  stone  revolves,  it  will  have 


Fig.   76 

a  tendency  to  carry  the  lens  with  it.  By  pinching  the  lens  a  little 
with  the  thumb  and  forefinger  of  the  right  hand,  and  guiding  it 
with  the  thumb  and  forefinger  of  the  left  hand,  the  speed  can 
be  regulated  at  will.  \\"ith  this  method  the  lens  should  be  cut 
fairly  close,  and  also  have  a  perfect  shape.  If  the  lens  is  not 
symmetrical  it  must  first  be  shaped  up,  using  the  method  before 
described  and  illustrated  by  Fig.  73,  page  64.     As  one  becomes 


The  Making  of  a  Mechanical  Optician  69 

more  expert  in  grinding  one  will  see  that  it  is  very  essential  to 
have  the  lenses  well  cut,  and  cribbed  into  shape. 

In  the  last  method  described,  one  really  handles  the  lens  just 
as  though  it  were  in  a  machine,  and  no  pattern  was  used.  In  this 
way  the  lens  follows  the  original  shape,  and  in  grinding  we  only 
put  on  a  bevel. 

The  correct  method  of  rimless  grinding  by  hand  is  shown 
in   Fig.  75,  page  65.     The  beginner  usually  finds  it  most  con- 


venient to  .stand  a  little  to  the  left  of  the  stone  and  hold  the 
lens  in  the  right  hand  between  the  thumb  and  fore  and  middle 
fingers  (Fig.  76).  In  this  method  the  lens  is  ground  at  a  point 
on  the  stone,  very  near  the  top.  The  movement  is  a  long,  sweep- 
ing motion,  using  the  entire  arm  from  the  shoulder.  First 
start  with  the  lens  held  so  that  it  touches  near  the  lower  end, 
then  move  it  downward  in  the  opposite  direction  to  that  in  which 
the  stone  is  turning,  and  roll  it,  so  to  speak,  as  far  as  possible. 
This  should  carry  the  lens  to  the  other  end,  thereby  having 
ground  one  side.  A  new  hold  is  taken  to  turn  around  the  end, 
then  a  new  start  for  the  other  side.  In  this  way  it  requires  about 
four  turns  to  complete  one  revolution.  If  there  is  any  shaping 
to  be  done  it  must  be  looked  after  at  this  time,  and  after  each 
sweep  of  the  lens  it  should  be  inspected  for  shape.  As  one  be- 
comes experienced,  this  will  require  only  a  second  or  two,  and 
really  the  grinding  can  almost  be  watched  on  the  stone. 


"JO  The  Making  of  a  Mechanical  Optician 

After  the  lens  is  ground  to  the  approximate  size  by  this 
method,  the  shape  having  been  found  to  be  correct,  the  edge  will 
probably  be  more  or  less  uneven.  By  this  is  meant  that  there 
vr'iW  be  a  number  of  ridges  at  different  points  where  a  new  start 
was  made  when  changing  the  position  of  the  lens  in  the  hand. 
These  should  be  taken  out,  and  the  lens  given  a  finish  that  will 
appear  as  near  like  a  machine-ground  lens  as  we  can.  This  is 
possible  by  holding  the  lens  in  such  a  position  that  will  allow  the 
stone  to  cause  it  to  revolve  between  the  fingers.  The  correct 
way  is  the  same  as  illustrated  in  Fig.  75,  page  65,  but  some  of 
the  older  grinders  prefer  a  method  as  illustrated  in  Fig.  ~~. 
In  this  method  the  lens  is  held  by  the  two  fingers  of  both  hands 
in  such  a  manner  that  they  act  the  same  as  the  two  shafts  in  an 
automatic  machine.  The  thumb  of  one  hand,  or  both  if  preferred, 
is  placed  on  the  edge  to  act  as  a  stop  or  governor.  A  certain 
amount  of  pressure  must  be  used  on  the  surface  of  the  glass  to 
keep  the  glass  from  slipping,  and  if  the  thumb  is  not  used  to 
govern  it,  it  will  revolve  too  rapidly.  The  revolution  must  be 
as  regular  as  possible  in  order  that  the  shape  may  be  preserved 
as  well  as  producing  a  perfectly  flat  edge.  As  the  lens  is  ground 
in  this  manner  the  size  should  be  kept  in  mind,  so  that  it  will  not 
be  ground  too  small.  When  the  lens  is  just  to  size  the  sharp 
edges  should  be  run  off  as  usual,  and  as  heretofore  described. 

GRINDING  FRAMELESS  LENSES  BY  MACHINE 

After  the  lenses  are  in  position  start  the  machine  and  let  the 
lenses  down  to  the  stone. 

For  machine  the  lens  should  be  cut  a  little  larger  tlian  for 
hand  grinding,  usually  about  i  mm.  all  around  is  allowed.  The 
marked  places  on  the  lenses  for  cutting  are  used  to  center  the 
lenses  in  the  machine.  The  lenses  are  placed  in  the  centering 
device  with  the  cutting  lines,  together  with  a  piece  of  rubber  or 
wet  cardboard  between  them  to  keep  them  from  slipping.  Ex- 
treme care  must  be  used  to  see  that  these  are  placed  on  the  pads 
just  right  so  that  the  axes  and  centers  will  be  perfect.  A  little  slip 
at  this  point  will  spoil  your  lenses. 

The  two  principal  styles  of  centering  devices  now  used  are 
somewhat  similar  in  the  method  of  using,  but  radically  different 
in  construction.     One  such  device  is  constructed  on  the  clamp 


The  Making  of  a  Mechanical  Optician 


71 


idea,  and  is  forced  open  by  a  spiral  spring.  The  machines  fitted 
with  this  device  are  suppHed  with  a  thick  pad  resembling  a 
pattern  or  former  (Fig.  78),  slotted  on  the  back  to  engage  the 
pins  on  the  head  spindle  of  the  machine.  The  top  is  oval  in 
shape,  fitted  with  a  rubber  pad  in  the  center  and  at  each  end  is 
a  hole  to  engage  the  pins  of  the  centering  device. 


Fig.    78 


If  the  lenses  have  been  properly  marked  before  cutting  there 
will  be  no  difficulty  in  placing  them  on  the  pad  to  obtain  the 
correct  axis  and  center.  If  not,  it  will  be  noted  at  this  point  how 
essential  it  is  to  have  a  conspicuous  line  on  the  lens.  The  center- 
ing device  is  held  in  the  right  hand,  and  the  lens  in  the  left.  If 
two  or  more  are  to  be  inserted  rubber  washers  or  wet  cardboard 
pads  should  be  placed  between  them.  It  will  also  be  found  more 
convenient  to  place  them  together,  or  build  them  up  in  the  hands 
first,  and  then  place  them  on  the  pad  at  one  time.  When  placing 
them  on  the  pad,  see  that  the  line  passes  directly  over  the  holes 
in  the  pad,  and  that  the  center  comes  directly  in  the  center  of  the 
hole  in  the  middle  of  the  pad  also.  The  centering  device  is  then 
pressed  together  with  the  thumb  of  the  right  hand  and  held  in 
position  with  the  left  hand  while  the  set  screw  is  tightened.  The 
lenses  should  then  be  held  securely,  and  it  will  be  possible  to 
inspect  them,  and  see  if  they  have  been  placed  in  position  cor- 
rectly. On  the  top  of  the  prongs  of  the  centering  device  will  be 
found  two  holes,  through  which  the  line  on  the  lens  can  be  dis- 
tinguished, and  by  sighting  through  these  the  line  should  be  seen 
directly  in  the  center.  A  little  study  on  the  part  of  the  operator 
will  readily  convince  him  that  if  the  lens  has  been  placed  on  the 
pad  accurately  it  cannot  possiblv  grind  off  axis  or  center,  pro- 


72  The  Making  of  a  Mechanical  Optician 

vided  that  they  do  not  slip  in  the  machine.  If  the  lens  has  been 
placed  in  position  carelessly  it  cannot  grind  correctly  and,  there- 
fore, do  not  blame  the  machine  for  any  inaccuracy.  The  pattern 
can  be  selected  and  placed  on  the  head  spindle,  as  previously 
described,  and  the  gauge  set  for  the  size,  which  is  governed  by  the 
length  of  lens  to  be  ground. 

For  size  subtract  the  width  from  the  length  and  the  differ- 
ence will  indicate  the  number  of  the  pattern  to  be  used.  This  is 
placed  in  the  machine  and  the  gage  set  to  the  length  required. 
For  example,  to  grind  40  x  31,  the  difference  is  9.  Fit  this  pattern 
and  set  the  pointer  to  40  mm. 

When  the  lens  has  been  secured  in  the  centering  device,  it  is 
ready  to  place  in  the  machine.  Open  the  tail  spindle  with  the 
hand-wheel  so  that  there  will  be  plenty  of  room  to  place  the  lens 
in  position.  Be  particular  regarding  this  point,  for  if  for  any 
reason  the  lens  should  strike  any  part  of  the  machine  when  being 
inserted,  it  will  be  very  liable  to  slip,  thereby  throwing  it  off  axis, 
or  out  of  center.  Place  the  holes  in  the  pad  over  the  pins  on 
which  the  pattern  or  former  has  been  placed,  and  when  set  cor- 
rectly, turn  the  hand-wheel  up  until  the  right  hand  pad  strikes 
the  surface  of  the  lens.  At  this  point  the  hand-wheel  will  turn 
very  easily,  or  in  other  words,  loosely,  so  that  it  will  appear  to 
slip.  It  can  then  be  given  a  turn  or  two  more,  very  lightly, 
until  the  hand-wheel  just  touches  the  spring  on  the  end  of  the 
tail  spindle.  Do  not,  under  any  circumstances,  turn  it  up  hard, 
for  it  will  not  only  do  no  good,  but  it  may  damage  the  machine, 
by  forcing  the  spring  out  of  place.  When  the  hand-wheel  has 
been  turned  up  in  this  manner  the  lens  is  secured  just  as  firmly 
as  it  can  be,  and  if  for  any  reason  it  should  slip,  it  will  be  because 
the  rubber  pads  do  not  hold  it  properly.  Either  the  rubber  has 
lost  its  elasticity,  or  else  they  may  have  become  covered  with 
grease.  In  this  case  clean  and  dry  tTiem,  or  fit  new  ones.  In 
fitting  new  pads,  secure  them  with  sealing  wax,  as  this  is  the 
best  method. 

The  lens  should  then  be  let  down  to  the  stone  gently  and 
allowed  to  grind  around  once  with  a  slight  spring  tension,  to 
remove  any  sharp  points.  After  one  revolution  has  been  made 
turn   the   left   hand-wheel,   which   regulates   the   spring  tension. 


The  Making  of  a  Mechanical  Optician 


73 


until  a  firm,  even  tension  is  obtained.  A  quarter  turn  will  be 
sufficient,  altbougb  tliis  will  be  regulated  by  tbe  number  of  lenses 
to  be  ground.  A  single  lens  will  require  only  a  very  sligbt  amount 
of  spring  tension,  whereas  two  pairs  can  be  forced  a  little  more. 
The  amount  of  spring  tension  used  will  regulate  the  speed  of 
grinding,  although  the  speed  of  the  stone  must  also  be  correct. 
Another  centering  device  is  constructed  similar  to  a  pair  of 
tongs.  This  is  held  in  the  left  hand,  and  opened  by  squeezing 
the  handle  together.  In  this  type  of  machine  the  pattern  or 
former  answers  also  for  the  pad,  having  a  rubber  washer 
cemented  on  the  face  (Fig.  79).  This  pad  also  has  holes  to 
engage  the  pins  on  the  centering  device,  and  the  first  opera- 
tion  is  to   select   the   correct   pattern,    and    place   it   in   position 


Fig.    79 


in  the  centering  device.  The  lens  is  then  laid  on  this  pad  with 
the  axis  and  center  in  the  correct  position,  as  before  described 
in  the  other  model.  By  releasing  the  pressure  on  the  handle  in 
the  left  hand,  the  lens  is  secured.  This  type  of  machine  is  opened 
by  pulling  the  liand  lever  towards  you  a  certain  amount,  to  allow 
the  lens  to  be  inserted  without  striking.  The  spring  is  then 
hooked  up  by  a  chain,  the  links  being  so  arranged  that  each  one 
increases  the  spring  tension.  All  other  directions  apply  to  this 
machine  as  well,  except  the  size  gauge,  which  is  set  by  pointer 
instead  of  a  micrometer  arrangement. 

Remember  that  in  operating  a  machine  the  one  point  to 
keep  in  mind  is  to  use  plenty  of  water  and  do  not  allow  the 
stone  to  run  drv. 


74  The  Making  of  a  Mechanical  Optician 

The  tension  should  also  be  regulated  according  to  the  number 
of  lenses  grinding  at  a  time.  If  too  much  is  used  for  a  single  lens 
it  will  chip.  The  time  necessary  to  grind  a  pair  of  lenses  will  vary 
from  four  to  ten  minutes,  depending  on  the  thickness  and  the 
amount  allowed  for  grinding.  Plenty  of  time  should  be  given, 
however,  because  if  they  are  removed  before  they  are  finished,  the 
shape  will  be  irregular.  You  can  easily  tell  when  they  are  finished 
by  the  sound.  It  is  unnecessary  to  remove  them  immediately,  how- 
ever, as  they  can  grind  no  smaller  than  the  gage.  After  they  are 
ground  to  size  they  must  be  removed  and  the  sharp  edges  taken 
off  the  same  as  if  ground  by  hand. 

When  the  lenses  are  removed  from  the  machine,  they  should 
be  wiped  immediately,  or  the  grindstone  grit  is  apt  to  dry  on  the 
surface,  and  when  cleaned  off  it  leaves  marks  resembling 
scratches.  These  are  very  difficult  to  remove,  but  thev  will  come 
off  with  a  wet  cloth  and  fine  pulverized  pumice. 

Lenses  can  be  edged  in  the  machine  without  cutting  if  de- 
sired, but  this  is  of  no  advantage  unless  grinding  for  stock.  Some 
opticians  prefer  to  use  their  machines  this  way  rather  than  allow 
them  to  stand  idle,  but  there  is  no  advantage  in  it,  as  interchange- 
able lenses  can  be  obtained  of  the  jobbers  at  about  the  same  cost. 

The  greatest'  difficulty  experienced  in  grinding  by  machine  is 
the  slipping  of  the  lenses.  This  is  caused  by  the  pads  becoming 
soft  and  greasy.  It  is  a  good  idea  when  through  with  the  machine 
for  the  day  to  place  a  piece  of  blotting  paper  between  them  to 
absorb  the  moisture  and  prevent  sticking. 

When  placing  concave  lenses  in  the  machine  make  sure  that 
the  pads  between  the  lenses  are  thick  enough,  otherwise  the  edges 
will  touch,  causing  them  to  crack. 

If  flat  places  or  lines,  called  facets,  are  found  on  the  edge,  the 
stone  is  out  of  true  and  should  be  turned  immediately. 

Some  prefer  to  use  the  frameless  machine  without  a  pattern, 
and  when  grinding  this  way  the  lenses  must  be  watched  to  see 
that  they  are  not  ground  too  small.  This  method  is  perhaps 
quicker,  but  the  machine  requires  constant  attention. 

In  cutting,  twice  as  much  should  be  allowed  on  the  ends  as  on 
the  sides  (unless  your  machine  has  a  compensating  device).  For 
example,  to  grind  40  x  31,  the  lens  should  be  cut  41  x  31^. 

Providing  you  do  grind  nearly  all  your  lenses  by  pattern,  it  is 
often  convenient  to  match  odd  or  special  shapes  by  this  method. 


CHAPTER  VIII 


DRILLING 


Glass  can  be  drilled  in  various  ways,  either  with  a  hand  drill 
or  with  power;  with  steel  point  or  diamond;  in  an  upright  drill 
or  in  a  lathe. 

For  drilling,  a  diamond  is  recommended,  and  this  can  be 
obtained  in  a  white  splint,  carbon  (black  diamond),  white  turned 
diamond,  or  a  turned  carbon.  A  white  splint  costs  about  five 
dollars,  although  a  better  one  can  be  obtained  from  six  to  eight 
dollars ;  carbon  about  ten  dollars ;  white  turned  diamond  about 
twelve  dollars ;  turned  carbon  from  fifteen  to  eighteen  dollars. 
We  recommend,  however,  the  best  white  splint,  as  it  has  a  rough 
point  and  cuts  faster.  It  can  also  be  sharpened  at  a  less  expense. 
Turned  diamonds  do  not  cut  as  fast,  but  are  less  liable  to  break. 
By  using  care,  however,  one  need  never  break  any  diamond. 

A  diamond  drill  should  run  at  from  1600  to  2200  revolutions 
per  minute,  but  1800  is  recommended.  If  it  runs  too  fast. 
It  throws  the  lubricant  out  of  the  hole,  and,  consequently,  runs 
dry.  If  it  runs  too  slow,  too  much  pressure  is  required.  These 
two  points  are  really  the  cause  of  all  breakage. 

Before  starting  to  drill,  see  that  the  stop  is  set  so  that  the 
drill  point  just  clears  the  pin  on  which  the  lens  is  placed.  There 
should  be  just  space  enough  to  slip  a  card  easily  under  the  drill 
point.  The  gage  should  also  be  set  so  that  the  hole  will  be  the 
right  distance  from  the  edge.  For  regular  flat  lenses  this  distance 
is  .093.  Strong  conve.x  lenses  will  be  drilled  farther  in,  and 
strong  concave  lenses  nearer  the  edge. 

All  lenses  should  be  drilled,  however,  for  a  snug  fit  and  then 
broached  or  filed  the  least  bit  for  the  variations  of  the  strap.  The 
most  accurate  way  is  to  try  the  strap  on  the  lens  and  mark  it  in 
the  screw  hole  with  ink,  or  better  still,  with  a  sharp  steel  point. 
(This  can  be  made  from  an  old  rat  tail  file.)  In  most  of  the  large 
shops  the  drills  are  arranged  so  that  the  pressure  is  applied  by 
foot  power,  thereby  allowing  the  use  of  both  hands.  This  can 
be  arranged  very  easily  by  drilling  a  hole  through  the  bench  and 


76  Tlic  Making  of  a  Mechanical  Optician 

attaching  a  wire  to  a  foot  pedal  on  the  floor.  After  a  Httle  prac- 
tice it  will  be  found  that  the  foot  is  just  as  sensitive  as  the  hand. 

There  are  a  great  many  drilling  fluids  on  the  market,  and, 
as  these  are  cheap,  we  would  recommend  using  one  of  them 
rather  than  going  to  the  trouble  of  making  it.  The  theory  of  a 
lubricant  is  to  keep  the  drill  coOl,  and  in  lapidaries  water  is  used 
on  diamond  drills  for  drilling  all  kinds  of  stonee.  Turpentine, 
however,  is  supposed  to  soften  glass,  and  for  this  reason  it  is  used 
principally  in  making  these  preparations ;  "3  in  i  oil"  is  also  used 
very  successfully  by  many  opticians.  If  you  have  an  up-to-date 
drill,  with  a  centering  device,  you  will  set  the  gage  and  place  the 
lens  in  position  between  the  four  pins,  apply  the  lubricant  and 
place  a  slight  pressure  on  the  handle.  Do  not  drill  right  straight 
down,  however,  but  raise  the  drill  constantly  to  allow  the  lubricant 
to  flow  into  the  hole.  If  it  runs  dry  it  will  show  a  white  powder 
and  more  fluid  must  be  applied.  This  is  the  most  particular  point 
in  drilling  and  must  be  watched  constantly.  The  breaking  of  a 
drill  is  usually  due  to  carelessness. 

If  you  find  that  the  lens  has  a  tendency  to  vibrate,  the  point 
of  the  drill  is  out  of  true  and  should  be  attended  to  immediately. 
This  is  due  to  the  breaking  off  of  a  small  part  of  the  stone,  making 
the  point  out  of  center.  This  can  be  sharpened,  however,  pro- 
viding the  point  is  not  too  short.  When  buying  a  new  drill,  be 
sure  that  the  setting  fits  the  hole  in  the  spindle  perfectly.  If  it  is 
small  the  set-screw  will  throw  it  out  of  center. 

After  the  lens  is  drilled  half  way  through,  turn  it  over  and 
drill  from  the  other  side.  If  it  is  drilled  above  center  it  will  be 
necessary  to  change  the  gage  governing  the  center  device  to  the 
opposite  side. 

Tories  cannot  be  drilled  in  a  regular  centering  device  unless 
it  has  a  tipping  table  or  other  attachment  to  tilt  the  lens.  If  a 
drill  is  used  without  an  attachment  of  this  kind,  the  centering 
device  should  be  removed  and  the  lens  held  in  the  hand.  The 
lens  should  be  tilted  up  when  drilling  the  concave  side,  and  down 
on  the  conve.x. 

Lenses  can  be  drilled  just  as  well  without  a  centering  device, 
but  it  is  necessary  to  dot  the  lens.  This  can  be  done  by  the  eye, 
or  a  separate  centering  device  for  marking  can  be  obtained  for  a 
small  sum. 


The  Making  of  a  Mechanical  Optician  JJ 

A  steel  point  will  drill  just  as  good  a  hole  as  a  diamond,  but 
it  is  necessary  to  sharpen  it  after  drilling  every  few  holes.  A 
good  point  can  be  made  from  an  old  rat  tail  file  sharpened  to  a 
long  point,  having  two  rounded  sides.  In  grinding,  however,  be 
careful  not  to  draw  the  temper.  A  steel  drill  should  run  much 
slower  than  a  diamond,  or  from  600  to  800  revolutions  per  minute. 
The  centering  device  should  not  be  used,  but  the  lens  should  be 
held  in  the  hand,  and,  instead  of  being  held  rigidly,  it  should  be 
rocked  slightly  to  allow  the  drill  to  cut. 

After  you  have  drilled  both  sides  of  the  lens  so  that  the  holes 
meet,  it  should  be  broached  out.  For  this  purpose  a  regular  four- 
sided  steel  broach  is  used,  and  is  fitted  in  one  end  of  the  idler" 
shaft.  These  will  have  to  be  replaced  occasionally,  as  they  become 
dull  and  break  the  lenses.  Some  drills  are  supplied  with  a  broach, 
similar  to  a  rat  tail  file,  but  these  are  used  in  the  same  way. 

Hand  drills  are  not  as  satisfactory  as  power  drills,  but  are 
used  successfully,  however,  by  opticians  wishing  to  drill  occa- 
sionally and  who  have  no  power.  We  recommend  running  these 
by  a  foot  wheel,  as  better  results  can  be  obtained.  The  great 
difficulty  with  these  drills  is  that  you  cannot  get  speed  enough, 
and  although  a  slow  speed  will  do  for  a  steel  drill,  it  does  not 
work  well  with  a  diamond.  When  using  them,  however,  more 
time  must  be  allowed  for  drilling,  as  it  is  not  well  to  force  it. 

We  frequently  hear  of  cases  where  opticians  require  from 
three  to  five  minutes  to  drill  a  hole.  In  cases  of  this  kind  there 
is  something  wrong;  either  the  speed  is  not  right  or  else  the 
diamond  needs  sharpening.  If  a  drill  is  working  right  a  hole  can 
be  drilled  in  five  to  ten  seconds. 

Opticians  often  make  the  mistake  of  using  a  very  long  dia- 
mond drill.  This  is  not  necessary,  and  they  are  very  liable  to 
break.  It  is  much  better  to  use  a  short  one  for  all  ordinary  lenses 
and  have  an  extra  one  for  thick  ones.  Do  not  forget  that  dia- 
monds are  not  guaranteed  against  breakage,  and  if  you  get  one 
that  is  not  right,  exchange  it  at  once. 

Although  the  drilling  of  glass  is  very  simple,  many  opticians 
seem  to  experience  quite  a  little  difficulty  in  this  work.  The 
trouble  may  occasionally  be  with  the  workman,  but  more  often 
it  is  the  fault  of  his  tools.  To  do  good  work  and  prevent  break- 
age one  should  have  a  good  drill.    This  not  onlv  means  the  dia- 


78 


The  Making  of  a  Mechanical  Optician 


mond  or  whatever  kind  of  a  point  he  may  use,  but  the  machine 
itself  should  be  as  good  as  can  be  bought. 

All  the  best  drills  are  fitted  with  centering  devices  and  this 
feature  alone  not  only  assures  one  of  accurate  work,  but  saves  a 


Fig.  80 — Universal  Drill    (Standard  Optical   Co.) 

great  amount  of  time.     We  are  illustrating  a   few  of  those  in 
common  use  to  show  the  method  of  using. 

Fig.  80  is  the  Universal  and  is  fitted  with  a  tilting  table  for 
the  drilling  of  torics.  To  drill  a  pair  of  flat  lenses  it  is  only 
necessary  to  open  the  centering  device  with  the  left  hand  and 
place  the  lens  in  position  between  the  four  pins.  Be  sure  the  lens 
is  placed  so  that  it  touches  all  four,  for  if  it  does  not  the  lens 
is  not  in  straight,  consequently  the  hole  will  be  drilled  ofif  center. 
To  guard  against  this  it  is  well  to  open  and  shut  the  centering 


The  Making  of  a  Mechanical  Optician  79 

device  once  or  twice,  so  the  lens  may  be  jarred  into  position, 
so  to  speak.  When  it  is  secured  between  the  four  pins  push  the 
centering  device  to  right  with  the  left  hand,  until  the  edge  of  the 
lens  comes  in  contact  with  the  gauge.  This  should  have  been  set 
at  the  correct  distance  previously. 

With  this  machine  is  a  small  steel  washer  with  several  holes 
drilled  at  different  distances  from  the  edge,  one  side  being  for 
plus  lenses  and  the  other  for  minus  lenses.  These  holes  are 
numbered  to  correspond  with  those  on  the  gauge  of  the  drill. 
There  is  also  a  small  pin  furnished  to  insert  in  the  holes  in  the 
strap.  The  idea  of  this  device  is  that  the  holes  in  the  strap  can 
be  measured  and  the  gauge  set  at  the  proper  distance.  Most  op- 
ticians, however,  set  their  drills  at  the  standard  distance,  which 
is  .093  and  for  new  work  this  will  be  correct,  and  on  the  old 
work  the  strap  can  be  measured  or  judged  as  you  prefer.  Straps 
are  made  so  accurate  at  the  present  time  that  very  little  variation 
will  be  found,  and  the  old  ones  are  usually  so  much  longer  that 
they  can  be  detected  at  a  glance  and  the  necessary  allowance  made 
for  them. 

When  the  gauge  has  been  set  correctly  and  the  lens  pushed 
up  against  it,  you  are  ready  to  drill.  Right  here  it  may  be  well 
to  add  a  few  words  of  caution  in  regard  to  the  placing  of  the  lens  • 
in  position.  In  the  first  place  be  sure  that  there  is  a  proper  bevel 
on  the  edge  of  the  lens,  especially  a  strong  concave.  By  this  we 
do  not  mean  that  the  lens  must  necessarily  have  a  very  conspic- 
uous bevel,  but  on  the  other  hand  it  must  not  have  a  sharp  edge. 
If  the  edge  is  too  sharp  it  will  chip  very  easily  and  if  perhaps  it 
does  not  chip  when  placed  between  the  pins  it  certainly  will  when 
pushed  against  the  gauge. 

Another  point  that  must.be  looked  after  is,  when  a  convex 
lens  is  being  placed  in  position  care  must  be  used  to  see  that  the 
thin  edge  is  not  pushed  under  the  gauge.  This  sometimes  happens 
and  even  if  it  is  not  chipped,  it  will  make  the  hole  come  too  far 
from  the  edge.  Care  should  also  be  used  to  see  that  every  lens 
lies  flat  on  the  table  and  that  one  side  is  not  tipped  up,  for  when 
the  drill  strikes  the  surface  of  the  lens  it  will  naturally  have  a 
tendency  to  force  it  into  position,  and  this  also  is  very  apt  to  cause 
chipping.  Be  sure  that  the  lens  lies  flat  on  the  little  pad  directly 
under  the  drill,  as  this  is  most  essential  and  the  fault  of  manv  of 


8o  The  Making  of  a  Mechanical  Optician 

the  old  style  drills  was  that  they  did  not  have  the  correct  bearing 
directly  beneath  the  drill  point. 

If  the  lens  is  to  be  drilled  on  center  it  is  only  necessary  to 
apply  the  pressure  with  the  right  hand,  lubricate  the  point  with 
drilling  fluid  and  drill  halfway  through.  Then  turn  the  lens 
over  and  drill  the  opposite  side. 

At  this  time  we  will  add  a  few  instructions  regarding  the 
sound  of  a  drill.  Learn  to  drill  by  the  sound  of  the  point  cutting 
the  glass.  Just  as  soon  as  the  diamond  point  comes  in  contact 
with  the  surface  of  the  lens  a  peculiar  grinding  noise  is  heard  and 
as  the  pressure  is  applied  and  the  point  sinks  into  the  glass  this 
sound  can  be  followed.  As  the  ear  is  trained  you  can  readily  tell 
when  the  drill  is  halfway  through  the  lens.  The  lens  is  then 
turned  over  and  placed  in  position  as  before,  but  this  time  be  sure 
that  the  hole  is  directly  under  the  drill  point.  If  the  drill  is 
accurate  and  if  you  placed  it  in  the  correct  position  in  the  first 
place  there  will  be  no  trouble.  If  some  mistake  was  made,  how- 
ever, the  holes  will  not  meet  and  a  very  poor  job  will  be  obtained. 
As  the  pressure  is  applied  on  the  second  side  notice  the  sound  as 
before  and  when  the  drill  goes  through  into  the  first  hole  it  can  be 
detected  instantly.  In  this  way  a  lens  is  very  rarely  broken  in  the 
drilling,  as  the  operator  knows  just  when  to  release  the  pressure. 

We  have  spoken  of  the  sound,  and  though  this  is  most  es- 
sential we  must  not  forget  the  hand  or  foot  that  applies  the 
pressure.  As  one  becomes  experienced  it  will  be  seen  that  they 
seem  to  work  together.  In  otHer  words,  it  almost  appears  as  if 
one  could  hear  with  the  hand,  as  they  work  so  in  harmony. 

When  the  hole  has  been  drilled  through  it  must  be  broached 
out,  as  will  be  seen  by  the  accompanying  illustration.  This  will 
also  give  an  idea  of  the  correct  shape  of  a  drill  point.  Fig.  8i 
shows  the  correct  shape  of  a  hole  that  has  been  drilled  with  a 
wedge-shaped  point.  In  this  way  the  hole  is  tapered  and  is  rarely 
broken  in  drilling  or  mounting;  also  it  is  much  more  substantial 
when  mounted.  When  it  is  run  on  the  broach  the  center  only  is 
cleaned  out  and  the  hole  is  left  as  in  Fig.  82.  A  hole  drilled  with 
a  straight  drill  with  a  flat  point,  as  in  Fig.  83,  is  not  only  very 
liable  to  break  in  drilling,  but  also  after  it  is  mounted.  In  drilling 
when  the  two  holes  meet,  the  drill  goes  through  with  a  jump, 
and  the  shock  often  breaks  the  lens.     If  it  does  not  break  in  all 


The  Making  of  a  Mechanical  Optician 


8i 


cases,  a  great  many  are  chipped  around  the  hole.  When  a  hole  of 
this  kind  is  drilled  and  then  run  on  the  broach,  it  is  also  not  only 
liable  to  break  if  it  is  not  well  lubricated,  but  it  dulls  the  broach 
very  quickly  and  a  dull  broach  will  cause  more  breakage  than 
almost  anything  else. 

Some  of  the  interchangeable  lenses  ground  at  the  factory 
often  have  fairly  straight  holes  and  these  are  drilled  this  way 


■7— 

» 

\    < 

X 

/ 

\ 

\ 
V 

1 

Fig.   81 

\ 

1 

1 
1 
1 

1 

1 
1 

^ 
^ 

Fig.    82 

Fig.   83 

for  the  reason  that  they  make  better  looking  lenses.  A  counter- 
sunk hole,  while  more  practical  and  always  used  in  prescription 
work,  does  not  make  the  best  looking  one,  whereas  a  straight 
hole  makes  a  neat  looking  lens. 

In  the  prescription  shops  it  is  customary  to  countersink  these 
holes  a  little,  thereby  taking  ofif  the  sharp  edges.  A  countersink 
can  be  made  of  steel,  a  rat-tail  file  will  do,  and  should  be  ground 
to  a  blunt  wedge-shaped  point.  This  can  be  used  in  a  lathe  or 
bv  hand,  by  twisting  it  between  the  fingers. 

In  drilling  above  the  center  in  this  machine  the  lens  is  placed 
in  position  between  the  pins  as  before.  After  it  is  secure,  release 
the  catch  in  the  front  with  the  right  hand  and  swing  the  table  to 
the  notch  marked  the  amount  you  wish  to  drill  above.  Some  of 
these  are  graduated  in  millimeters  and  others  in  inches ;  they  can 
be  had  either  wav.    The  lens  is  then  drilled  halfway  through,  then 


82 


The  Making  of  a  Mechanical  Optician 


turned  over  and  the  catch  turned  to  the  opposite  side,  thereby 
swinging  the  table  as  before.  It  is  perhaps  safer  and  more  ac- 
curate, especially  for  the  beginner,  to  return  the  table  to  the 
central  position  after  drilling  one  side.  In  this  way  one  can  see 
to  the  centering  of  the  lens  much  better  than  when  the  table 
is  set  at  an  angle. 

For  torics  the  lens  should  be  placed  in  position  with  the 
table  in  the  central  position  and  swung  into  position  afterward. 


Fig.  84 Factory  Drill  of  American  Optical  Co. 


otherwise  it  is  almost  impossible  to  place  the  lens  accurately  with 
the  table  tilted  upwards  or  downwards.  The  correct  way  is  to 
tilt  the  table  downwards  first,  then  place  the  lens  in  position  with 
the  table  in  a  central  position.  The  table  can  then  be  twisted  the 
desired  amount.  After  drilling  this  side,  tilt  the  table  upwards 
and  turn  it  to  the  central  position  for  the  centering,  afterward 
twisting  the  table  to  the  correct  position  for  the  hole  to  come 
directly  under  the  drill  point. 

The  A.  O.  Co.  Factory  drill  (  Fig.  84 )  is  constructed  some- 
what differently,  having  an  arrangement  with  two  bent  fingers, 


The  Making  of  a  Mechanical  Optician 


83 


if  we  mav  thus  term  them,  instead  of  the  four  pins.     At  the  left 
is  a  lever  which  is  operated  with  the  left  hand  to  open  the  fingers 


Fig.   85 — Globe  Drill 

to  engage  and  center  the  lens.  Directly  beneath  this  is  a  cylinder 
which  is  graduated  for  the  drilling  otT  center.  The  method  of 
using  this  drill  is  to  set  it  for  the  desired  amount  off  center,  then 


Fig.  86 — King  Drill 

with  the  left  hand  swing  the  table  forward  a  little,  opening  the 
arms  to  engage  the  lens  at  the  same  time.  The  lens  is  then  in- 
serted and  centered  and  swung  back  against  the  post  or  gauge. 


84  The  Making  of  a  Mechanical  Optician 

Tories  are  drilled  on  this  machine  by  raising  and  lowering 
two  little  slides  on  the  front  part  of  the  arms. 


Fig.  87 — Hand  Drill 

Drill  Fig.  85  is  one  of  the  ordinary  styles.  The  centering 
arrangement  is  constructed  with  four  pins  and  is  very  simple.  For 
drilling  above  and  below  it  is  only  necessary  to  slide  the  table 
forward  or  backward  the  desired  amount.  For  drilling  torics  the 
centering  device  must  be  removed,  and  the  lens  dotted  for  proper 
position  of  the  hole. 

There  are  many  styles  of  power  drills  on  the  market,  some 
having  no  centering  devices  at  all.  These  drill  just  as  well  as  the 
better  ones,  but  more  experience  is  required.  One  drill  just  re- 
cently placed  on  the  market  takes  the  place  of  a  hand  drill  where 
no  power  can  be  obtained,  as  it  can  be  run  with  dry  cell  batteries 
(Fig.  86).  The  regular  batteries  are  used  and  the  motor  does  not 
start  until  the  lever  is  pressed  downward. 

There  are  many  good  hand  drills,  ^\'e  are  illustrating 
(Fig.  87)  one  of  the  higher-priced  ones  and  some  of  these  can  be 
operated  with  a  diamond  drill  if  desired.  The  only  difficulty 
experienced  is  that  it  is  very  difficult  to  obtain  speed  enough. 


CHAPTER  IX 


MOUNTING 

Mounting,  or  "setting-up,"  as  it  is  usually  called  in  the  pre- 
scription shops,  is  a  branch  of  the  mechanical  work  that  requires 
considerable  experience.  Almost  anyone  can  screw  a  pair  of 
glasses  together,  but  this  is  not  mounting  in  any  sense  of  the  word. 
The  principal  feature  is  to  be  able  to  fit  a  lens  securely,  with  all 
the  parts  bearing  properly,  and  yet  so  there  is  absolutely  no 
liability  of  breakage. 

Breakage  is  not  only  expensive,  but  causes  more  annoyance 
and  delay  than  anything  in  the  business.  One  doing  this  part  of 
the  work  must  necessarily  be  conscientious,  whether  they  are 
working  for  themselves  or  for  someone  else.  If  one  has  one's 
mind  on  one's  work,  one  can  easily  tell  when  the  screw  is  inserted 
whether  it  is  too  tight  or  not.  The  trouble  with  most  workmen 
is  that  the  screw  is  driven  home  as  if  it  were  a  piece  of  wood, 
rather  than  glass.  When  a  strap  is  properly  fitted  it  should  be 
possible  to  twist  it  sideways  just  a  little,  until  the  last  turn  of 


Fig.  88 

the  screw,  or  until  it  is  set  up.  The  last  turn  should  make  a  snug 
fit.  If  the  screw  turns  hard  from  the  start,  breakage  is  sure 
to  be  the  result. 

In  order  to  do  good  work  one  must  have  good  tools.  There 
are  many  grades  of  pliers  on  the  market  to-day,  and  where  for- 
merly any  pair  that  could  be  obtained  in  a  hardware  store  an- 
swered the  purpose  we  are  now  using  tools  that  are  made  as  good 
as  surgical  instruments.     All  jobbers  carry  regular  optical  pliers 

85 


86 


The  Making  of  a  Mechanical  Optician 


in  stock,  and  although  the  cost  may  be  slightly  more,  they  will 
last  for  years.  These  are  well  tempered  and  the  round  and  snipe 
nose  can  be  tapered  to  very  fine  points  and  still  stand  hard  work. 
The  No.  35  strap  plier  is  the  most  essential  (Fig.  88).  One 
pair  will  answer  the  purpose,  but  the  best  workmen  usually  have 


Fig.  89 

two  pairs,  with  difterent  lengths  of  lips.  Although  these  are  made 
in  one  lengfth,  it  is  a  very  easy  matter  to  grind  off  the  lip  slightly 
on  an  emery  wheel,  and  then  smooth  it  with  an  emery  or  buti' 
stick.  In  this  way  one  can  have  a  very  short  one  for  the  jobs 
that  require  very  little  fitting,  and  yet  should  be  eased  a  little  to 
prevent  the  strap  bearing  too  tightly  on  the  edges.    The  one  with 


Fig.  90 


the  longer  lip  can  be  used  where  the  strap  must  be  made  consid- 
erably thinner.  These  pliers  can  be  ordered  from  the  jobber  in 
this  way  if  desired. 

A  new  plier,  known  as  No.  45  crimpling  plier  (Fig.  89),  has 
just  been  placed  on  the  market,  and  this  tool  will  not  only  be 
found  very  convenient  in  all  shops,  but  it  will  prevent  many  lenses 
from  being  discarded.  In  drilling  lenses  it  quite  frequently  hap- 
pens that  the  hole  is  too  near  the  edge,  and  also  many  times  old 
lenses  will  be  poorly  drilled.  When  fitting  a  new  mounting  it  is 
necessary  to  shorten  the  strap  to  fit  it  perfectly.     This  plier  ac- 


The  Making  of  a  Mechanical  Optician 


87 


complishes  the  desired  effect  at  one  operation,  and  in  such  a  way 
that  it  cannot  be  detected. 

The  other  necessity  is  the  snipe-nose  (Fig.  90).  Round  and 
flat  noses  are  convenient  for  some  operations,  but  can  be  dispensed 
with.  The  snipe-nose  should  be  tapered  ahnost  to  a  point,  and  the 
inside  of  the  jaws  should  be  perfectly  smooth  and  polished.  The 
sharp  edges  should  also  be  removed.     This  can  be  done  with  a 


Fig.  91 

fine  emery  stick  with  very  little  trouble.  Under  no  conditions 
should  a  corrugated  jaw  be  used,  as  this  marks  everything  you 
touch  with  it. 

We  should  advise  all  pliers  to  be  purchased  in  nickel,  as  they 
not  only  look  better,  but  are  much  smoother  to  handle.  A  medium 
size  is  also  to  be  preferred,  although  many  opticians  are  using 
the  larger  sizes.  These  are  all  right  for  bridge  bending,  especially 
for  workmen  with  large  hands,  but  as  frameless  straps  are  much 
more  easily  bent  than  bridges,  the  smaller  ones  are  more  con- 
venient. 

In  mounting  lenses  speed  is  quite  essential,  especially  if  one 
attempts  to  do  all  his  own  work,  as  well  as  refracting.     For  this 


Fig.  92 


reason  we  are  touching  on  some  small  points  which  may  seem 
trifling,  but  it  is  just  the  knack  of  handling  tools  that  makes  one 
workman  excel  over  others.  In  the  large  prescription  shops  the 
man  who  has  the  proper  tools  and  knows  how  to  use  them,  wiH 
easily  be  noticed  by  the  way  he  handles  them. 


88  The  Making  of  a  Mechanical  Optician      « 

Cutting  pliers  are  made  in  many  styles.  The  older  style? 
(Figs.  91  and  92),  are  just  as  satisfactory,  as  long  as  they  are 
kept  in  good  condition.  The  trouble  in  most  shops,  however,  is 
that  one  pair  of  pliers  is  used  for  everything.  To  do  good  work 
one  should  have  a  pair  of  cut  glass  screws  only,  and  keep  them  for 
that  purpose.  For  cutting  heavy  steel  wire  and  for  the  odd  jobs,  a 
heavier  pair  should  be  used.   The  Chappel  cutting  plier  (Fig.  93), 


Fig.  93 


is  used  extensively,  as  this  cuts  close  to  the  strap,  and  requires 
no  finishing.  This  plier  is  so  constructed  that  the  edges  do  not 
come  together,  and  in  this  way  they  keep  their  cutting  edge  for 
a  long  time. 

There  are  also  several  styles  of  spring  cutters  (Fig.  94)  on 
the  market,  and  the  advantage  of  these  is  that  the  screw  is  not 


Fig.  94 

cut  with  a  snap.  According  to  theory,  a  lens,  if  mounted  properly. 
will  not  break  when  the  screw  is  cut,  but  many  of  them  cut  with 
such  a  snap  that  the  jar  would  iiaturall\-  cause  some  breakage. 
Others  have  a  tendency  to  crawl  towards  the  strap,  if  the  screw 
is  cut  too  close,  and  thereby  seem  to  pull  the  screws  slightly. 


The  Making  of  a  Mechanical  Optician 


89 


Whatever  plier  is  used,  however,  must  be  in  good  condition  to  do 
good  v^'Ork. 

Rat-tail  files  (Fig.  95  ),  should  be  of  the  best  quality,  and  well 
tapered.    Some  are  quite  blunt,  and  cannot  be  inserted  in  the  hole, 


Fig.   95 


Fig.   96 


except  at  the  top.  A  good  file  should  be  fairly  small  and  should 
protrude  through  the  lens  about  an  inch.  The  cut  is  optional, 
but  should  not  be  too  coarse.  No.  o  is  quite  coarse.  No.  i  medium, 
and  No.  2  is  as  fine  as  can  be  used,  and  yet  cut  fast  enough.  If 
a  coarse  file  is  used  care  must  be  taken  to  prevent  chipping. 

A  glass  screw  tap  (Fig.  96)  will  be  needed,  not  only  to  ease 
the  thread  in  the  stud,  but  also  to  insert  through  the  straps  and 
lens  for  a  preliminary  trial.  It  is  well  to  have  two  of  these,  one  to 
be  kept  for  tapping  the  strap,  and  the  other  can  be  an  old  one ;  in 


^!4^S^ 


Fig.   98 


Fig.  97 

fact,  one  that  has  the  thread  worn  considerably  is  to  be  preferred, 
as  it  is  then  inserted  easily  and  quickly.  If  one  has  a  tap  plate 
these  can  be  made  without  much  trouble,  but  as  they  can  be  pur- 
chased from  the  jobber  for  about  twenty-five  cents  it  hardly  pays. 
They  are  made  usually  from  Stubbs's  steel.  They  are  threaded 
about  one-half  inch,  and  are  then  flattened  on  three  sides,  some- 


Fig.  99 

what  tapering,  then  hardened.  A  broach  holder  (Fig.  97),  or  pin 
vise  (Fig.  98),  will  be  required  to  hold  the  tap,  and  those  with 
the  wooden  handle  are  better  for  inserting  through  the  strap  and 
lens,  whereas  the  regular  pin  vise  is  preferable  for  tapping  the 

strap. 

A  swivel  top  screwdriver  is  the  best  for  mounting,  as  m 
mounting  it  is  necessary  to  turn  the  screw  in  and  out  usually 
several  times.     If  a  regular  wooden  handle  spec  .'screwdriver  is 


90 


The  Making  of  a  Mechanical  Optician 


used,  it  requires  more  time,  as  a  new  grip  must  be  taken  at  every 
half  turn.  In  the  prescription  shops  a  man  using  a  screwdriver 
of  this  kind  would  be  so  slow  that  he  could  never  expect  to  hold 
his  position.  We  are  illustrating  several  styles  of  this  in  common 
use  (Figs.  99  and  loo),  the  wooden  one  being  quite  popular  on 


Fig.  100 


account  of  its  lightness.  These  should  be  used  with  the  swivel  in 
the  palm  of  the  hand,  and  not  the  way  a  watchmaker  usually  does, 
^lany  opticians  have  been  watchmakers  and,  in  fact,  are  doing 
watchmaking  in  connection  v^^ith  their  optical  business  to-day ; 
consequently,  it  is  natural  for  them  to  get  in  the  habit  of  using 
a  screwdriver  with  the  forefinger  on  the  swivel,  twisting  the 
barrel  between  the  ne.xt  finger  and  the  thumb.  This  in  the  optical 
business  is  quite  awkward,  and  the  work  cannot  be  done  as  con- 
veniently or  as  well. 

If  one  uses  the  old  style  of  cutting  pliers  it  will  be  necessary 
to  have  a  fine  flat  half-round  file  to  finish  the  screws.  The  half- 
round  is  illustrated  (Fig.  loi),  as  this  is  better  for  bridges  where 
the  shank  interferes.     If  the  Chappel  cutters  are  used,  the  file 


Fig.  101 

will  not  be  needed.  !Many  opticians  use  the  screw-finisher  in  a 
polishing  head,  or  lathe,  and  although  these  produce  the  best 
finish,  it  requires  a  little  skill  to  keep  them  in  shape.  This  will  be 
explained  later. 


Fig.  102 

There  are  many  other  tools  that  are  in  use  that  can  be  added 
to  this  equipment,  if  they  suit  the  individual  taste.  Among  these 
are  the  No.  39  plier  for  angling  the  straps  of  studs  or  temples ; 
the  cushion  pad.  on  which  the  lens  can  be  placed  when  inserting 
the  screw. -and  hand  broach,  a  hand  countersink;  also  a  hand  tap- 


The  Making  of  a  Mechanical  Optician  91 

ping  machine.  A  very  convenient  thing  is  a  large  size  tap  with 
a  quantity  of  large  glass  screws  for  repairing  old  straps  where 
the  thread  has  been  stripped,  and  an  Ajax  wrench  (Fig.  102), 
with  screws  and  nuts  for  Ajax  straps.  These  nuts  are  sometimes 
used  when  the  thread  in  the  strap  has  been  stripped,  and  also  as 
locks  for  the  glass  screws.  Buff  sticks  and  wheels  are  used  by 
some  opticians  to  finish  the  straps,  but  now  this  is  usually  dis- 
pensed with. 

It  is  well  to  have  a  good  assortment  of  screws.  This  should 
include  gold,  gold-filled  and  German  silver,  in  regular  length  and 
extra  long,  also  Ajax  and  the  large  size,  as  these  are  used  on 


Fig.  103 

repair  jobs  almost  entirely.  When  fitting  new  lenses  to  old  gold 
mountings  the  optician  can  hardly  afford  gold  screws,  and  the 
filled  answer  the  purpose  just  as  well.  A  complete  assortment  of 
screws,  in  glass  bottles,  can  now  be  obtained  in  a  neat  little  case 
(Fig.  103).  These  are  inexpensive  and  are  not  only  convenient, 
but  save  considerable  waste.  When  a  stock  of  screws  are  carried 
in  open  boxes  or  envelopes  they  are  sure  to  get  mixed,  and  often 
upset  and  lost. 

Before  trying  the  lens  in  the  strap  it  will  be  necessary  to 
remove  the  screws  from  the  mountings,  and  as  these  are  inserted 
at  the  factory  by  machine,  they  will  probably  work  hard.  The 
screw  holes  should  then  be  tajjped  f)ut  so  that  the  screws  enter 
easily. 

After  the  holes  in  the  lens  are  drilled  and  broached  and  the 


92  The  Making  of  a  Mechanical  0['tician 

studs  tapped,  the  next  operation  is  to  try  the  strap  on  the  lens. 
If  the  lens  is  thinner  than  the  strap  it  will  fit  into  the  bottom  of 
the  strap.  Notice  whether  the  parts  of  the  strap  that  bear  on  the 
edge  conform  with  the  curve  of  the  lens.  If  not,  shape  them 
with  the  snipe  nose  pliers.  Then  take  an  old  tap  or  a  pin  about 
the  same  size  and  insert  it  in  the  screw  hole  so  that  if  passes 
through  the  glass  into  the  screw  hole  of  the  opposite  strap.  If 
the  lens  has  been  drilled  properly,  it  will  be  just  a  little  too  tight. 
Now  remove  the  glass  and  file  the  hole  just  a  grain  toward  the 
edge  of  the  glass  with  a  rat  tail  file  lubricated  with  drilling  fluid. 
Insert  the  lens  again  and  try  a  second  time.    If  an  old  tap  is  used 


3SS 


Fig.  104 

it  acts  the  same  as  a  screw,  so  that  when  it  is  screwed  into  the 
hole  you  can  easily  judge  whether  it  is  too  tight  or  not.  If  it 
appears  the  least  bit  tight  do  not  try  to  force  it,  but  remove  it  and 
file  the  hole  a  little  more.  For  this  reason  a  small  metal  screw- 
driver, with  a  swivel  top,  is  recommended,  rather  than  a  wooden 
handle  one,  as  you  do  not  get  such  a  good  purchase  on  the  screw. 
You  can  then  tell  readily  if  it  binds.  One  of  the  greatest  mistakes 
is  made  in  forcing  screws  in  the  mountings,  as  this  is  responsible 
for  most  all  the  breakage. 

When  the  tap  enters  the  hole  easily  and  there  is  no  play,  the 
screw  can  be  inserted,  and  as  it  is  turned  in  try  the  strap  and  see 


Fig.    105 


Fig.    106 


if  it  is  tight.  When  a  strap  is  properly  fitted  it  should  be  possible 
to  twist  it  sideways  just  a  little  until  the  last  turn  of  the  screw, 
or  until  it  is  set  up.  The  last  turn  should  make  the  snug  fit.  If 
the  screw  turns  hard  from  the  start,  the  hole  in  the  glass  should 
be  filed  a  little  more. 

W'e  have  now  taken  it  for  granted  that  the  lens  and  strap 
were  just  the  right  thickness   (Fig.   104).     If  the  strap  is  too 


The  Making  of  a  Mechanical  Optician  93 

narrow  the  lens,  perhaps,  will  go  in  but  half  way.  We  then  take 
the  strap  plier  and  insert  the  plain  jaw  in  the  strap  and  the  jaw 
with  the  hook  on  the  outside  (Fig.  105).  With  a  slight  pressure 
the  strap  will  be  widened  a  little,  and  if  the  lens  is  still  tight 
repeat  the  operation  on  the  other  side  of  the  strap.  This  opera- 
tion was  formerly  done  with  a  snipe  nose  plier  before  the  inven- 
tion of  the  strap  plier.  The  great  difficulty  experienced  with  this 
tool  was  that  the  straps  were  thrown  out  of  alignment  and  it  was 
necessary  to  square  them  up  and  tap  them  over  again.  With  the 
strap  plier  this  is  not  only  unnecessary,  but  the  work  can  be  done 
much  more  quickly. 

If  the  lens  is  thinner  than  the  strap  the  plier  is  inserted  with 
the  hook  on  the  inside  and  the  plain  jaw  on  the  outside  (Fig.  106  j. 
This  will  make  a  slight  kink  in  the  strap,  very  close  to  the  lens- 
bearing  parts,  which  is  hardly  noticeable.  In  selecting  straps, 
however,  it  is  best  to  use  one  that  is  a  little  snug  and  open  it  with 


Fig.  107 

the  strap  pliers  than  to  use  one  that  has  to  be  made  much  nar- 
rower. A  convex  lens  is,  of  course,  thicker  at  the  screw  hole 
than  at  the  edge,  and  for  this  reason  the  strap  will  be  made  nar- 
rower at  the  bottom  (Fig.  107),  otherwise  it  will  twist  sideways. 
A  concave  lens  is  just  the  opposite,  and  the  strap  should  be  made 
narrower  at  the  screw  holes  with  a  snipe  nose  plier.  The  lens 
should  be  inserted  on  the  side  at  the  thinnest  part  and  slipped 
along  to  the  screw  hole.  In  f.tting  strong  lenses,  especially  con- 
cave, see  that  there  is  a  good  bevel  on  the  edge  near  the  screw 
hole  to  prevent  flanking. 

If  the  hole  has  been  drilled  too  near  the  edge  it  will  be 
necessary  to  bend  down  the  lens-bearing  parts  and  a  little  varia- 
tion does  not  matter  materially,  but  if  there  is  any  space  to  speak 
of  these  ears  should  be  bent  with  a  slight  kink  near  the  post  (Fig. 
loS).  This  can  be  done  with  the  strap  pliers,  but  care  should  be 
used  not  to  take  up  too  much.  Under  no  circumstances  bend  the 
points  down,  lea,ving  an  opening  between  the  lens  and  the  strap 
(Fig.  109).  as  this  will  work  loose  almost  immediately.  In  some 
cases  where  the  strap  has  been  opened  as  much  as  it  will  stand 


94  The  Making  of  a  Mechanical  Optician 

in  fitting  strong  concave  lenses,  or  if  the  workman  does  not  have 
a  pair  of  strap  pliers,  it  will  be  necessary  to  file  the  edge  of  the 
lens  to  allow  it  to  go  into  the  strap,  but  this  method  should  not 


Fig.  108 

be  used  unless  absolutely  necessary.     It  is,  however,  desirable  to 
do  this  on  strong  concave  lenses. 

In  fitting  torics  the  strap  should  be  bent  with  the  snipe  nose 


Fig.  109 

pliers  to  conform  to  the  curve  of  the  glass  (Fig.  no).  Although 
this  is  really  no  more  difficult,  most  opticians  prefer  to  send  the 
mountings    to    the    prescription    houses    and    have    these    lenses 


The  Making  of  a  Mechanical  Optician  95 

mounted,  as  the  lenses  are  expensive,  and  if  one  is  broken  it  takes 
away  the  profit.  Occasionally  an  old  pair  of  lenses  is  sent  in  to 
be  fitted  with  new  mountings  and  the  holes  are  so  large  that  it  is 
impossible  to  fit  a  strap  so  that  it  will  look  well.  In  cases  of  this 
kind  a  plug  of  tinfoil  or  of  wood  can  be  inserted  in  the  hole 
nearest  the  edge  of  the  lens  and  this  will  take  up  the  space 
between  the  lens  and  the  lens-bearing  parts  of  the  strap.  There 
are  also  strap  tighteners  on  the  market  for  this  purpose. 

There  is  also  a  device  on  the  market  supposed  to  prevent 
breakage  and  this  is  used  when  fitting  expensive  lenses,  such  as 
fused  bifocals.  This  consists  of  a  rubber  tube  and  a  glass  screw, 
with  a  long  pin  on  the  end  of  the  threaded  part.  After  the  screw 
is  set  up  it  should  be  cut  off  and  finished.  If  a  screw  finisher  is 
used  the  end  should  be  left  a  little  long  to  allow  for  rounding. 
If  it  is  cut  too  short  the  tool  will  cut  into  the  strap.  If  you  do 
not  use  a  screw  finisher,  cut  the  screw  fairly  close  and  file  the 


Fig.  110 

end  with  a  flat  file  almost  down  to  the  strap.  A  piece  of  card- 
board, or  a  brass  plate  having  a  square  place  cut  out  for  the  strap, 
should  be  used  to  lay  over  the  glass  to  prevent  the  file  from 
scratching.  There  is  also  a  new  plier  on  the  market  for  this  work 
which  cuts  the  screw  so  close  that  it  does  not  require  filing. 

If  the  optician  does  his  own  drilling  he  can,  of  course,  drill 
lenses  to  suit  himself.  There  are,  however,  a  great  many  who 
order  lenses  drilled  and  do  the  mounting  themselves.  Many  of 
these  opticians  believe  that  lenses  should  be  drilled  so  that  all  that 
is  necessary  to  do  is  to  screw  them  into  the  mounting.  If  lenses 
were  drilled  this  way  a  great  many  would  fit  too  loose,  and  a 
poor  job  would  be  the  result.  The  right  way  is  to  have  them  all 
a  little  snug  and  then  fit  them  as  before  described.  To  do  this 
a  complete  set  of  tools  is  necessary  and  care  should  be  used  in 
fitting.  If  the  optician  would  only  realize  that  men  doing  the 
mounting  in  prescription  jobs  are  the  most  expert  optical  work- 
men and  have  spent  years  learning  the  trade,  there  would  not  be 
very  many  complaints  regarding  the  drilling. 


96 


The  Making  of  a  Mechanical  Optician 


The  mounting  of  frameless  lenses  is  a  trade  in  itself  and  too 
much  care  cannot  be  used  in  selecting  the  thickness  of  lenses  and 
straps.  The  strap  plier  has  simplified  the  mounting  of  frameless 
lenses  wonderfully  and  some  opticians  have  a  wrong  idea  of  this 
tool.  It  is  not  only  designed  to  bend  a  strap  from  2  mm.  to  4  mm., 
or  vice  versa,  but  it  should  be  used  in  place  of  the  snipe  nose  plier 
in  fitting  almost  every  lens.  In  large  shops  the  men  mounting 
rimless  work  have  two  pairs,  one  with  a  short  hook  for  the  regu- 
lar jobs  and  one  with  a  long  hook  for  extreme  cases. 

There  are  opticians  who  have  an  idea  that  all  frameless  lenses 
should  be  so  accurately  drilled  that  no  fitting  should  be  required. 
Although  lenses  are  drilled  to  a  standard  gauge  and  straps  are 
milled  the  same,  it  is  impossible  to  have  them  fit  perfectly.  A 
slight  variation  in  the  size  of  the  diamond  point  will  change  the 
size  of  the  hole ;  also  some  lenses  are  countersunk  and  others 
are  drilled  straight,  as  before  explained.  As  a  rule,  if  all  lenses 
were  drilled  so  they  could  be  readily  screwed  into  the  strap,  the 
strap  would  work  loose.  In  order  to  give  good  satisfaction  to 
the  wearer  the  lenses  should  be  perfectly  tight,  and  yet  not  so 
snug  that  breakage  will  be  the  result.  If  one  is  in  the  habit  of 
ordering  lenses  from  the  prescription  houses,  unmounted,  he 
should  expect  to  do  a  certain  amount  of  fitting,  and  in  order  to 
do  this  he  should  have  a  proper  equipment  of  tools. 


VJZU 


Fig.  Ill 


We  have  already  explained  in  preceding  articles  the  method 
of  adjusting  the  strap  with  strap  pliers.  Many  opticians  still  use 
the  old  method  of  bending  the  strap  with  snipe-nose  pliers,  how- 
ever, and  although  on  the  average  the  work  is  not  so  well  done, 
we  will  give  an  explanation. 

The  strap,  of  course,  should  be  slightly  wider  than  the  lens, 
but  just  enough  so  the  lens  will  slip  in  easily.  If  it  is  too  wide, 
grasp  one  side  of  the  strap  with  the  point  of  the  pliers  in  the 


The  Making  of  a  Mechanical  Optician  gj 

middle  and  bend  it  slightly  outwards.  This  will  make  a  slight 
kink  near  the  lens-bearing  part  (Fig.  ii  i  ).  Now  bend  it  backward 
to  its  original  position  and  you  will  find  that  it  has  made  the 
opening  slightly  narrower.  By  repeating  the  operation  on  the 
other  side  of  the  strap  both  sides  will  be  alike  and  the  strap  will 
be  made  uniformly  narrower.  The  strap  should  then  be  sighted 
endwise,  to  see  if  the  sides  of  the  strap  are  parallel,  as  in  bending 


Fig.  112 

them  with  a  plier  of  this  kind,  they  are  very  apt  to  be  out  of 
alignment.  After  bending  them  parallel  the  screw  holes  should  be 
tapped,  and  this  will  also  have  a  tendency  to  bring  them  in  line 
the  other  way.  It  is  very  necessary  to  have  the  strap  in  as  per- 
fect condition  as  possible,  for  if  it  is  bent  out  of  line  in  any  way 
breakage  is  sure  to  be  the  result. 

One  of  the  great  advantages  of  the  strap  pliers  is  that  they 
accomplish  this  result  without  altering  the  original  alignment  of 
the  strap.  This  operation  is  for  convex  lenses  (Fig.  28)  and  in 
making  the  inner  part  of  the  strap  narrower  we  prevent  the  lens 
twisting.  If  this  is  not  properly  done,  or  the  lens  is  fitted  in  the 
strap  with  the  jaws  parallel,  it  is  possible  to  hold  any  eyeglass 
or  spectacle  by  grasping  both  lenses  and  twist  it  out  of  shape. 
This,  in  many  cases,  is  the  cause  of  lenses  flaking  near  the  strap. 

If  the  strap  is  too  narrow  it  must  be  opened  to  admit  the 
lens  sufficiently,  and  yet  not  bind  on  the  edges.  In  most  cases 
concave  lenses  require  this  operation  and  it  is  very  difficult  to  fit 
them  properly,  without  the  strap  binding  on  the  edge  of  the  lens, 
if  it  is  not  done  with  a  strap  plier.  In  opening  the  strap  grip 
one  side  as  near  the  bottom  as  possible ;  that  is,  near  the  lens- 
bearing  part,  and  open  the  strap  outwards  as  before.  Remember, 
however,  that  for  the  convex  lenses  we  grip  it  near  the  middle, 
whereas  for  concave  we  grip  it  as  far  back  as  possible. 

When  the  strap  has  been  spread  on  one  side  (Fig.  112)  grip 


98  The  Making  of  a  Mechanical  Optician 

it  near  the  middle  and  bend  it  back  to  its  original  position.  It  will 
then  be  noticed  that  this  side  has  been  somewhat  rounded  out. 
By  repeating  this  operation  on  the  opposite  side  quite  a  little  extra 
width  can  be  obtained.  Sight  the  strap  endwise  and  straighten  as 
before  explained. 

Some  of  the  newest  style  bridges  have  an  invisible  foot ;  in 
other  words,  the  shank  is  soldered  in  a  depression  on  one  side 
of  the  strap.  In  this  style  it  is  practically  impossible  to  bend 
the  side  on  which  the  bridge  is  soldered  and,  consequently,  all  the 
variation  must  be  made  on  the  opposite  side. 

In  doing  this  the  strap  will  be  shortened  somewhat  and  it 
will  probably  be  necessary  to  file  the  hole  slightly  to  prevent  the 


Fig.  113 

screw  binding.  If  the  lens  is  concave  and  it  is  found  that  it  binds 
slightly  in  the  bottom  of  the  strap,  it  will  be  well  to  file  the  edges 
slightly,  to  allow  for  the  rounding  of  the  strap. 

When  filing  a  lens  lay  it  on  the  edge  of  the  bench  perfectly 
flat,  with  the  hole  towards  you.  Hold  it  with  the  left  hand  and 
with  a  rat-tail  file  which  has  been  dipped  in  drilling  fluid  file  a 
\'-shape  slot  from  the  hole  to  the  edge  of  the  lens.  Unless  a  very 
fine  file  is  used,  this  will  cut  very  rapidly,  so  care  must  be  used 
not  to  get  it  deeper  than  is  necessary.  A  little  filing  on  both  sides 
is  to  be  preferred,  rather  than  all  on  one  side.  Care  must  also 
be  used  to  see  that  the  point  of  the  file  does  not  cut  on  the  opposite 
side  of  the  hole  fFig.  113  ),  as  this  makes  a  very  bad  looking  job. 
In  doing  this  work  always  use  a  rat-tail  file,  as  this  produces  a 
V-shape  slot  and  takes  off  that  part  of  the  glass  that  binds.  It 
must  be  remembered,  however,  that  in  filing  a  lens  it  is  weakened 
considerably,  and  with  the  strap  pliers  it  is  very  rarely  necessary. 
If  this  must  be  done,  however,  take  off  as  little  as  possible. 


The  Making  of  a  Mechanical  Optician 


99 


In  fitting  concave  lenses  where  the  strap  is  wide  enough  to 
take  the  lens  without  filing,  the  strap  can  be  bent  edge-shape  and 
the  lens  inserted  on  the  thin  edge,  and  you  can  then  slide  it  around 
to  the  hole.  In  this  way  the  strap  is  right  down  into  position  and 
requires  no  bending.  When  the  edge  must  be  filed  to  take  the 
lens  it  is  impossible  to  do  this,  consequently  the  strap  must  be 
forced  over  the  edge.  A  pair  of  pliers  with  one  long  curved  jaw 
(Fig.  114)  is  very  convenient  to  press  the  strap  into  position  after 
the  lens  has  been  inserted. 


Fig.  114 

If  the  hole  has  been  drilled  too  near  the  edge  the  lens-bearing 
parts  must  be  bent  down  to  conform  to  the  curvature  of  the  lens. 
This  operation  has  been  described  with  the  regular  pliers,  but 
the  No.  45  crimpling  plier  now  accomplishes  this  result  with  one 
operation  and  in  such  a  way  that  it  cannot  be  detected.    This  is 


>¥ 


Fig.  115 

made  with  a  slot  in  one  jaw,  which  is  inserted  over  on  side  of 
the  strap.  It  is  also  shaped  to  fit  the  lens-bearing  parts.  The 
opposite  jaw  has  an  opening  which  fits  around  the  post,  and  when 
the  pressure  is  applied,  it  forces  the  lens-bearing  parts  downward, 
thereby  shortening  it  slightly.    When  the  lens  is  inserted  no  open- 


lOO 


The  Making  of  a  Mcchaiiicci!  Optician 


ing  can  be  seen,  as  it  is  covered  by  the  side  of  the  strap.  The 
accompanying  illustration  (Fig.  115  )  shows  a  poorly  fitted  strap; 
also  one  that  has  been  formed  with  this  plier.  It  is  impossible  to 
say  too  much  regarding  the  fitting  of  straps,  as  the  number  of 
poor  jobs  in  use  to-day  is  almost  a  disgrace  to  the  profession.  In 
the  last  few  years  the  work  has  been  greatly  improved,  however, 
and  this  is  especially  noticeable  when  one  considers  the  number 
of  straps  and  other  devices  that  have  been  placed  on  tlie  market 
to  overcome  this  defect. 

Ajax  straps  do  not  have  to  be  bent  in  this  way.  If  the  side 
of  the  strap  (there  is  but  one  in  this  style")  has  been  bent  back- 
wards the  tendency  is  to  bend  the  lens-bearing  parts  down,  the 
same  as  a  regular  strap,  but  this  way  is  incorrect.  Bv  bending 
the  side  upwards  a  little — in  other  words,  make  the  angle  of  the 
side  of  the  strap  and  the  lens-bearing  parts  more  acute,  the  lens 


r:^ 


Fig.  116 


will  fit  properly.  If  the  hole  in  the  lens  is  just  the  right  distance 
this  should  be  a  right  angle,  but  even  if  it  is  not,  it  will  make 
no  material  difference. 

Some  opticians  grind  oft'  the  edge  slightly  when  the  hole  has 
been  drilled  too  far  from  the  edge.  This  not  only  requires  extra 
time,  but  also  changes  the  shape  of  the  lens  slightly.  It  is  much 
better  and  more  convenient  to  file  the  holes,  as  it  cannot  be  de- 
tected and  is  just  as  strong. 

In  mounting  many  workmen  have  their  own  peculiar  ways  of 
fitting  straps.  For  example,  if  the  screw  binds  slightly  at  the 
start  the  pressure  can  be  relieved  by  pressing  firmly  with  the  side 
of  the  screwdriver  on  the  end  of  the  stud  or  strap.  This  forces 
the  lens-bearing  parts  back  .slightly  and  frequently  the  screw  will 
then  turn  easily.  If  there  is  a  slight  opening  on  the  sides  these 
can  be  closed  up  with  a  slight  pressure  of  the  snipe-nose  pliers 
on  the  strap.  Pliers  for  this  purpose  can  be  made  by  grinding 
out  the  inside,  so  there  is  no  danger  of  edge-chipping  by  the 


The  Making  of  a  Mechanical  Optician 


lOI 


jaws  of  the  plier.  These  little  points  are  referred  to  only  to  show 
how  it  is  possible  to  increase  the  speed,  but  they  are  somewhat 
dangerous  for  the  inexperienced. 

TORICS 

Toric  are  no  more  difficult  to  mount  than  flat  lenses,  provided 
that  the  strap  is  bent  as  described  in  our  previous  articles.  All 
other  instructions  relating  to  flat  lefises  apply  to  this  form  of  lens 
also.  Do  not,  however,  attempt  to  fit  a  toric  lens  into  a  strap  that 
has  not  been  shaped  to  fit.  We  see  so  many  fitted  as  in  Fig.  ii6 
that  a  word  of  caution  is  necessary.  By  studying  this  drawing 
for  a  moment  one  can  easily  see  the  causes  of  so  much  breakage 
in  mounting  these  lenses. 


Fig.  117 


The  best  method  of  finishing  the  ends  of  screws  is  with  a 
screw  finisher.  There  are  two  kinds  on  the  market — the  upright 
(Fig.  117),  which  resembles  the  ordinary  drill  press,  and  the  hori- 
zontal (Fig.  118),  which  is  similar  to  a  buff  head.  The  upright 
supports  the  screw  a  little  better,  perhaps,  but  the  horizontal  is 
quicker.  In  using  these  machines  the  screw  should  be  cut  a  little 
long,  and  if  the  ordinary  cutting  pliers  are  used  the  bevel  on  the 


I02  The  Making  of  a  Mechanical  Optician 

jaw  will  leave  them  about  the  right  length.  If  the  close  cutters  are 
used  see  that  they  are  not  cut  too  short.  When  holding  the  screw- 
up  to  the  cutters  place  the  forefinger  or  thumb  against  the  screw- 
head  to  support  it  somewhat  and  rock  the  glass  slightly  to  prevent 
the  screw  cutting  to  a  point.  The  condition  of  the  knife  will  also 
have  considerable  to  do  with  the  shape  of  head.    The  knife  should 


Fig.  118 

be  honed  with  a  very  small  oil  stone,  having  a  rounded  edge,  and 
kept  as  sharp  as  possible.  When  inserted  in  the  holder  it  should 
be  adjusted  so  that  it  will  cut  just  enough  to  make  a  half-round 
head. 

If  the  horizontal  head  is  used  it  must  be  run  left-handed,  or 
in  other  words,  from  you.  All  the  cutters  are  made  to  cut  this 
way  and  many  are  out  of  use  to-day  that  have  not  given  satis- 
faction, for  the  reason  that  they  have  been  run  the  wrong  way.  It 
must  be  remembered  that  buff  heads  run  toward  you,  so  for  this 
reason  it  is  necessary  to  have  a  separate  machine  for  the  screw- 
finisher.  The  advantage  of  finishing  screws  in  this  way  is  that  it 
requires  no  polishing  and  also  forms  a  slight  burr  on  the  end  of 
the  screw,  and,  according  to  theory,  it  should  not  work  loose  as 
quickly.  Under  any  condition,  take  pride  in  having  your  work 
done  well  and  in  such  a  manner  that  if  it  is  taken  to  a  competitor 
for  repairs  it  will  bear  inspection  and  cannot  be  criticised. 


CHAPTER  X 


BIFOCALS 


Cement  bifocals  are  still  the  most  commonly  used,  for  the 
reason  they  are  the  lowest  in  price.  The  trade,  as  well  as  the 
public,  are  fast  becoming  educated  to  use  the  better  lenses,  how- 
ever, as  the  wonderful  increase  in  the  sale  of  Kryptoks  will  show. 
We  find  the  sale  of  stock  cement  bifocals  decreasing,  although  just 
as  many  cements  are  made  in  the  prescription  shops. 

The  first  step  in  making  a  pair  of  cement  bifocal  lenses  is  to 
select  the  stock.  The  distance  lenses  will  be  written  on  the  pre- 
scription and  although  any  form  of  lens  can  be  used,  it  will  make 
considerable  difference  in  the  price  of  some  combinations.  It  is 
also  desirable  to  place  the  wafers  next  the  eye,  if  possible,  as  it 
makes  the  reading  segments  more  invisible.  The  idea  of  adver- 
tising invisible  bifocals  has  not  only  proved  profitable  to  the  trade, 
but  has  improved  the  workmanship  on  the  cement  bifocals  and, 
incidentally,  driven  the  Perfection  and  Split  bifocals  from  the 
market. 

\\'hen  making  a  pair  of  sphericals,  periscopic  distance  lenses 
are  selected :  first,  on  account  of  the  better  form,  and  secondly, 
on  account  of  the  uniform  curvature  of  the  inside  surfaces.  This 
surface  on  American  ground  lenses  is  always  —  1.25  on  periscopic 
convex  lenses,  and  +  1.25  on  the  outside  of  periscopic  concave 
lenses.  With  concave  lenses  it  does  not  make  so  much  difference, 
as  we  will  show  later.  On  account  of  the  uniform  inside  surface 
of  pcx.  lenses,  the  factories  adopted  a  uniform  stock  of  wafers, 
having  a  -\-  1.25  surface  on  one  side,  and  the  balance  of  the  power 
on  the  other.  These  are  known  as  "regular  wafers"  and  are  or- 
dered by  this  term.  They  are  also  the  lowest  price  wafers  that 
are  manufactured. 

We  will  take,  for  example  (Fig.  119),  a  prescription  distance 
+  2,  reading  -|-  3.50,  or  it  may  be  written,  distance  +  2,  add  + 
1.50  for  reading.  We  select  a  pair  of  pcx.  lenses  +  2  and  a  pair 
of  regular  -\-  1.50  wafers.  These  wafers  will  be  +  1.25  on  one 
side  and  -j-  .25  on  the  other,  the  -(-  1.25  curve  will  be  cemented,  of 

103 


I04 


The  Making  of  a  Mechanical  Optician 


course,  to  the  —  1.25  surface  of  the  distance  lenses.  After  these 
are  cemented,  it  must  be  remembered,  tlie  contact  surfaces  (that 
is,  the  • —  1.25  and  the  -|-  1.25)  do  not  have  any  effect  on  the  power 
of  the  reading  portion.    We  simply  add  the  powers  of  the  outside 


>-3.tsr 


i-jzr 


+  zi~ 


h  tL. 


-f-3ro 

Fig.   119 


s-a 


surface  of  the  distance  lens  and  the  outside  surface  of  the  wafer, 
to  obtain  the  reading  power.  In  this  prescription  the  distance 
lens  being  -|-  2  and  having  an  inside  surface  of  —  1.25,  must,  of 
course,  have  an  outside  surface  of  -\-  3.25.     The  outside  surface 


-^/M 


7^/jr 


^"  uzso 


-i.ir 


of  the  wafer  being  -)-  .25,  we  have  the  desired  -{-  3.50  power. 
Many  opticians  seem  to  experience  quite  a  little  difficulty  in  figur- 
ing these  wafers,  but  if  the  contact  surfaces  have  no  effect,  except 
that  thev  must  be  the  same  in  order  to  fit  so  thev  can  be  cemented. 


The  Making  of  a  Mechanical  Optician  105 

there  will  be  no  trouble.  Take,  for  example  (Fig.  120),  a  prescrip- 
tion with  -)-  2  distance  and  +  2.75  reading.  The  wafer  in  this 
case  will  be  +  1.25  on  one  side  and  —  .50  on  the  other.  This  is 
really  a  compound  wafer,  but  as  the  factories  are  obliged  to  fur- 
nish all  combinations  of  "regular  wafers,"  you  really  obtain  them 
at  the  same  price. 

Now  suppose  we  had  selected  for  the  first  prescription  (Fig. 
121)  a  pair  of  double  convex  lenses  for  distance  +  2.  There 
would  have  been  -\-  i  on  each  side,  and  to  fit  a  wafer  we  must 
have  one  with  a  —  i  surface.  This  could  not  be  selected  from 
the  stock  of  regular  wafers,  as  there  would  be  no  such  combina- 
tion. As  we  must  have  this  curve,  it  must  be  surface  ground,  and 
to  make  the  required  addition  of  -(-  1.50,  we  must  have  on  the 
other  side  +  2.50.  We  then  have  a  combination  of  —  i  ^  + 
2.50,  and  this  we  call  a  compound  wafer,  for  the  reason  that  this 
form  is  used  to  fit  to  compound  lenses.  It  can  readily  be  seen 
that  the  price  will  be  the  same  as  if  fitted  to  compound  lenses, 
and  although  the  distance  lenses  cost  no  more,  the  extra  expense 
of  the  wafers  makes  the  job  cost  more  than  is  necessary.  Many 
times  a  prescription  is  sent  to  the  prescription  houses,  either 
ordering  double-convex  cement  bifocals,  or  else  the  optician  fits 
a  pair  of  double  convex  lenses  to  the  frame,  and  sends  them  in 
to  have  the  wafers  fitted,  and  then  is  unable  to  understand  the 
extra  charge. 

It  should  always  be  remembered  that  cement  bifocals  in  con- 
vex sphericals  should  always  be  ordered  pcx.,  or  if  no  specifica- 
tion is  made  they  will  be  made  in  this  form,  unless  for  some 
reason  double  convex  is  wanted,  in  which  case  the  e.xtra  charge 
will  be  made.  As  before  stated,  periscopic  concave  lenses  are  all 
made  with  a  -f-  1.25  outside  curve.  It  does  not  make  a  desirable 
form  to  fit  wafers  to  the  outside  of  these  lenses,  so  all  wafers  are 
fitted  on  the  inside,  consequently  they  must  be  ground  to  order. 
For  example,  we  will  take  (Fig.  122)  prescription  distance  — 
3.50,  reading  —  2,  the  reading  lenses  of  course  always  being  the 
weaker.  As  the  outside  curve  is  -|-  1.25  we  must  have  on  the 
inside  —  4-7S-  To  fit  this  surface  we  must  have  a  -\-  4.75  surface 
on  the  wafer :  the  other  surface  will  then  be  —  3.25.  The  combi- 
nation of  the  wafer  will  then  be  —  3.25  =  -(-  4.75.  This  is  a 
compound  wafer,  consequently  costs  extra. 


io6 


The  Making  of  a  Mechanical  Optician 


Now  suppose  we  select  for  this  same  prescription  (Fig.  123) 
a  pair  of  double  concave  lenses  —  3.50.  These  lenses  will  be  — 
1.75  on  each  side,  and  as  the  power  of  the  wafers  is  to  be  +  i-50. 
and  one  surface  must  be  +  1.75  to  fit  the  —  1.75  surface,  we  must 


7^  -J  SO 


-2..60 
Fig.  123 


■hl.oo 


'■/■J.i-0 


Fig.    124 


have  a  wafer  -j-  1.75  =  —  .25.  This  is  also  a  compound  wafer 
and  must  be  groupd  to  order,  the  same  as  the  first  form.  In  this 
case  it  will  be  seen  that  it  makes  no  difference  in  the  expense 
whether  they  are  made  in  the  double  concave  or  periscopic  con- 
cave form.  As  this  is  true  of  all  combinations  of  concave  cement 
bifocals,  as  well  as  those  having  a  concave  distance  and  convex 
reading,  it  makes  no  difference  as  far  as  the  expense  is  concerned, 
which  way  they  are  ordered.  As  the  periscopic  form  is  to  be 
preferred  and  there  is  no  difference  in  the  expense,  it  is  better 
to  make  them  this  way. 

Cvlinder  cement  bifocals  require  what  are  known  as  "piano 
wafers."  As  cylinders  have  one  side  piano  the  wafers  must 
necessarily  be  ground  in  such  a  form  that  one  side  will  be  piano 
and  these  surfaces  must  always  be  cemented  together.  Under 
no  circumstances  can  a  wafer  be  cemented  to  the  cylinder  surface 
of  a  lens,  as  this  will  destroy  the  cylinder  effect.  Although  it  is 
generally  understood  that  two  surfaces  to  be  cemented  must  be 
the  same  curve,  we  often  find  surfaces  cemented  that  are  not 
the  same  and  occasionally  we  find  wafers  cemented  to  the  cylinder 
surfaces.     According  to  theory,  this  is  impossible,  and  if  it  is 


The  Making  of  a  Mechanical  Optician 


107 


possible  to  make  them  hold  for  a  while  they  will  usually  come 
back  in  a  very  short  time  to  be  re-cemented.  When  a  job  is  re- 
ceived by  a  prescription  house,  with  the  complaint  that  the  cement 
does  not  hold,  the  surfaces  are  first  inspected  to  see  if  they  are 
correct,  and  in  many  cases  poor  contacts  are  the  cause.  In  select- 
ing wafers  for  cylinders  no  trouble  will  be  experienced,  for  the 
power  is  entirely  on  one  side.  For  example,  a  -|-  1.25  piano  wafer 
is  -|-  1.25  on  one  side  and  piano  on  the  other.  It  will  be  noticed, 
however,  that  a  +  1.25  piano  wafer  and  a  -(-  1.25  regular  wafer 
are  the  same. 

Compounds  require  special  wafers,  as  has  already  been 
stated,  and  although  these  seem  to  give  more  trouble  to  the  op- 
tician, they  are  really  just  as  simple.  If  one  point  will  be  remem- 
bered, it  will  help  to  simplify  the  figuring  of  these  wafers,  and 
that  is,  always  write  out  the  distance  and  reading  correction  in 
full,  and  the  surfaces  will  be  right  before  you.  For  example, 
take  a  prescription  distance  +  2  ^  +  .50  ax.  90,  add  -\-  1.50  for 


•i-sa 


-3.5-0 


\fiio\ 


-loo 


Fig.   125 


jy  +lo»  ~-^  s'  »^  to 
Fig.    126 


reading.  If  we  attempt  to  figure  the  surfaces  of  the  wafers  from 
this  prescription  it  is  somewhat  difficult.  If  we  write  the  pre- 
scription (Fig.  124) — 

Distance   -j-  2       =  -j-  .50  ax.  90 
Reading    -f-  3.50  =  -f  .50  ax.  90, 
we  already  have  the  inside  and  outside  surfaces  figured.     You 
will  remember  that  the  contact  surfaces  have  no  efTect,  conse- 
quently all  we  have  to  do  is  to  select  a  wafer  to  fit  the  -|-2  surface 


io8 


The  Making  of  a  M echanical  Optician 


of  the  compound,  which  will  be  —  2;  the  other  surface  will  be 
the  reading  power,  which  is  +  3.50.  As  the  two  outside  surfaces 
will  give  the  reading  power,  it  will  be  seen  that  the  outside 
surface  of  the  wafer  is  +  3.50  and  the  outside  surface  of  the 
compound  is  +  .50  ax.  90,  and  we  have  the  reading  correction, 
-(-  3.50  =  -\-  .50  ax.  90.  This  is  true  of  all  compounds  whether 
-(-  ^  -(-,  —  =^  — ,  -(-  =  —  or  —  ^  +,  and  to  illustrate,  take 
for  example  (  Fig.  125  )  prescription  distance  —  3.50  =  -|-  .50  ax. 
90,  reading  add  -(-  1.50.     This  prescription  will  be  as  follows: 

Distance   —  3.50  =  +  .50  ax.  90 
Reading    +2       ^  +  .50  ax.  90. 

The  wafers  will  have  a  -)-  3.50  surface  to  tit  the  distance  lens, 
and  —  2  for  the  reading  power.  When  cemented  the  outside  of 
the  distance  lens  will  be  +  .50  ax.  90  and  the  outside  of  the 
wafers  —  2 ;  hence  we  have  the  reading  correction  —  2  =  -|-  .50 
ax.  90.  In  making  compound  cement  bifocals  it  is  customary  to 
fit  the  wafers  next  the  eyes,  whenever  possible,  in  order  to  make 
them  inconspicuous.     The  rule  in  most  pre.scription  houses  is  to 


■)*/«♦« 


-i  I4  „  o    -   — l^<ut   ^  o 

Fig.    127 


+  too 


-/"    l-tl  oa 


Fig.    128 


I)lace  iheni  inside,  whenever  the  reading  power  is  less  than  -j-  4.50, 
and  when  it  is  .stronger  it  is  placed  on  the  outside.  It  is  necessary 
to  use  your  judgment,  however,  it  being  poor  form  to  jilace  a 
-j-  ■=  —  compound  or  any  lens  having  a  concave  surface,  with 
the  weaker  surface  out. 


The  Making  of  a  Mechanical  Optician  109 

Tories  are  somewhat  more  complicated,  unless  the  prescrip- 
tion is  transposed  so  the  spherical  surface  is  inside.  If  the  pre- 
scription is  not  written  in  this  way  it  should  tirst  be  transposed 
and  the  rest  will  be  simple.  For  example,  take  (Fig.  126 )  prescrip- 
tion distance  -f-  2  =  +  .50  ax.  90,  reading  add  +  1.50,  this  will  be 

Distance   +2       =  +  .50  ax.  90 
Reading    +  3.50  =  +  .50  ax.  90 

The  distance  lens  if  ground  on  a  +  6  curve  would  be  -f  6  =  + 
6.50  on  the  outside  and  —  4  inside.  To  fit  this  surface  we  must 
have  a  -f  4  curve,  as  the  power  of  the  wafer  is  -f  1.50;  we  sub- 
tract this  from  the  -+-  4  and  we  have  —  2.50.  By  then  referring 
to  the  outside  surfaces  we  find  that  the  distance  lens  is  +  6  =  + 
6.50,  and  the  wafer  is  —  2.50.  The  difiference  between  the  +  6 
a„a  —  2.50  will  give  the  reading  power  of  +  3.50  =  +  .50  ax.  90. 
In  this  case  it  will  be  seen  that  the  +  6  base  curve  must  always  be 
considered,  consequently  the  reading  power  is  always  obtained 
by  fitting  a  wafer  with  the  outside  surface  having  a  curve  of 
such  a  power  that  the  difference  between  this  surface  and  the 
base  will  equal  the  reading  prescription.  If  this  prescription 
(Fig.  127)  had  been  written  distance  +  2.50  =  —  .50  ax.  o, 
reading  add  +  1.50,  with  the  request  that  it  be  filled  as  written, 
and  not  transposed,  we  would  be  obliged  to  fit  the  wafers  on  the 
outside.  This  form  of  lens  would  have  —  6  =  —  6.30  on  the 
inside,  and  +  8.50  on  the  outside. 

As  we  have  already  explained,  a  wafer  cannot  be  cemented 
to  the  cylinder  surface,  as  it  will  destroy  the  cylinder  effect.  The 
outside  surface  being  +  8.50,  it  will  be  necessary  to  have  —  8.50 
surface  on  the  wafer  to  fit,  and  as  the  whole  power  of  the  wafer 
must  be  -f  1.50.  the  other  surface  will  be  -f  10.  \\'e  then  have 
the  combination  —  8.50  =  -f  10.  It  will  be  seen  these  are  ex- 
treme curves  and  are  not  only  hard  to  surface-grind  on  account 
of  the  extreme  thinness,  but  will  be  just  as  hard  to  edge  and 
cement.  A  job  of  this  kind  is  not  only  more  expensive,  but  as  a 
rule  a  number  of  wafers  are  broken  before  a  perfect  job  is 
obtained. 

Tn  making  toric  bifocals  it  is  always  preferable  to  transpose 
the  combinations  so  a  .spherical  surface  can  be  obtained  on  the 
inside,  even  though  it  is  a  weak  curve.     If  the  spherical  of  the 


no  The  Making  of  a  Mechanical  Optician 

distance  lenses  is  very  strong  the  full  inside  curve  can  be  obtained 
by  using  a  +  9  D.  base. 

All  combinations  of  torics  are  worked  out  in  the  same  way 
and  if  all  combinations  will  be  transposed  to  a  form  having  a  -\- 
cylinder  there  will  not  alone  be  less  trouble  in  figuring  the  wafers, 
but  the  curves  will  not  be  extreme. 

Occasionally  we  are  requested  to  make  a  pair  of  bifocals 
(Fig.  128)  as  follows:  Distance,  -j-  i  ^  +  .50  ax.  90;  reading, 
-(-  2  =  +  I  ax.  90.  This  combination  has  a  different  power 
cylinder  in  the  reading  correction,  and  although  it  may  be  con- 
trary to  the  rule  and  unnecessary,  it  can  be  made  by  fitting  two 
(2)  wafers,  one  on  each  side.  As  the  contact  surfaces  do  not 
count,  the  outside  surfaces  must  be  ground  to  produce  the  de- 
sired effect.  We  must  first  have  a  surface  —  .50  ax.  90  to  fit 
the  +  -50  a^-  90 ;  on  the  outside  we  will  then  grind  +  i  ax.  90. 

This  makes  a  wafer  with  two  cylinder  surfaces,  and  this  is 
not  only  difficult  to  grind,  but  is  very  expensive.  The  other  wafer 
will  be  a  regular  compound  form,  having  —  i  contact  to  fit  the 
-f-  I  sph.  surface  of  the  compound,  the  other  will  be  -)-  2.  We 
then  have  the  reading  correction,  -(-  2  =  -|-  i  ax.  90.  It  shows 
that  a  combination  of  this  kind  is  obtained  by  an  error  in  the 
refraction,  as  astigmatism  is  constant  and  does  not  change  for 
reading. 

Cross  cylinders  cannot  be  made  in  bifocals  and  these  com- 
binations should  be  transposed  to  compounds  and  wafers  fitted 
in  the  regular  way. 

CEMENT  BIFOCALS 

In  making  cement  bifocals  the  distance  lenses  are  ground 
the  same  as  usual,  except  that  when  grinding  to  frame  they  should 
be  left  a  little  large,  or  about  i  mm.  between  the  joints.  The 
wafers  are  about  30  mm.  round  in  the  rough,  and  if  the  prescrip- 
tion is  such  that  one  wafer  can  be  used  for  two,  it  should  be  split 
in  the  center,  using  a  hand  diamond  or  a  sharpened  rat  tail  file. 
They  can,  however,  be  edged  in  quantity  in  the  frameless  machine 
before  splitting,  but  care  should  be  used  not  to  screw  them  in  too 
tightly.  It  is  not  practical  to  attempt  to  edge  less  than  a  pair. 
If  ground  in  this  way  they  will  be  left  28  mm.  diameter  and  then 
cut  in  the  center. 


The  Making  of  a  Mechanical  Optician 


III 


It  is  always  advisable  to  center  wafers  when  possible,  and  if 
the  prescription  reads,  for  example,  distance  +  2,  reading  +  4, 
the  power  of  the  wafer  is  equal  to  the  distance.  As  a  spherical 
lens  is  practically  two  prisms  with  the  bases  together,  by  fitting 
the  wafer  with  a  thin  edge  upward  and  the  thick  downward,  the 


Fig.    129 


Fig.    130 


prismatic  power  is  neutralized  (Fig.  129).  When  the  power  of 
the  wafer  is  stronger  than  the  distance,  it  is  necessary  to  cut  it 
nearer  the  center  to  obtain  less  prismatic  power,  consequently 
two  wafers  must  be  used.  When  the  power  of  the  wafers  is 
weaker  than  the  distance  lens,  it  will  be  cut  as  far  from  the  center 
as  possible,  to  obtain  all  the  full  prism  power. 

It  is,  however,  practically  impossible  to  vary  this  very  much, 
as  the  wafers  are  not  large  enough.  The  only  way  that  this  can 
be  obtained  is  to  grind  prism  wafers.  It  is  not  absolutely  nec- 
essary to  do  this  as  a  little  variation  in  the  center  does  not  matter 
much  except  that  the  centers  must  always  be  on  the  same  hori- 
zontal plane.  In  other  words,  do  not  have  one  center  up  and  the 
other  down,  as  one  wafer  centered  and  the  other  not,  as  this  will 
cause  the  patient  quite  a  little  discomfort  perhaps,  and  when  they 
return,  complaining,  you  will  be  at  a  loss  to  know  the  cause  of  the 
trouble. 

When  fitting  piano  wafers  to  cylinders  with  the  axis  at  90°, 
always  cut  them  from  the  center  (Fig.  130). 

After  the  outside  edge  is  finished  (leaving  the  bottom  rough) 
it  is  ready  to  be  cemented.  Clean  the  distance  lens  and  the 
contact   surface    of    the    wafer   carefully    with    alcohol.      Put    a 


112  The  Makiinj  of  a  Mechanical  Optician 

small  drop  of  cement  on  the  lens  and  place  the  wafers  in  position. 
Hold  the  lens  over  an  alcohol  flame,  or  if  gas  is  used,  a  Bunsen 
burner.  Do  not  use  a  white  flame,  as  it  will  smoke  the  lens.  An 
ordinary  wood  spring  clothes  pin  is  very  convenient  for  holding 
the  lens,  or  tweezers  can  be  used.  Heat  the  lens  gradually  until 
the  cement  boils,  then  remove  it  from  the  flame  and  allow  it  to 
cool ;  at  the  same  time  place  the  wafer  in  position  with  a  stick 
or  tweezers,  being  careful  to  press  out  all  bubbles.  When  it  is 
cool,  see  that  it  is  firm  and  cannot  be  moved.  If  so.  the  cement 
was  not  cooked  enough.  If  it  appears  yellow  when  laid  on 
white  paper,  it  is  cooked  too  much  and  burned. 

There  is  another  method  of  cementing  where  the  cement 
is  prepared  first  and  in  this  way  it  is  necessary  to  cook  a  quantity 
of  cement  in  a  jar  slowly.  It  requires  quite  a  little  experience 
to  get  this  just  the  right  consistency.  The  cement  should  be 
cooked  so  that  it  is  quite  thick,  applying  it  to  the  lens  with  a  stick. 
With  this  method  it  is  only  necessary  to  warm  the  lens  and  spread 
the  cement  evenly  over  the  surface  as  though  it  was  ordinary 


Fig.    131  Fig.    132 

liquid  glue.     The  wafer  is  then  placed  in  position  and  allowed 
to  cool. 

Strictly  speaking,  all  wafers  should  be  set  in  i  mm.  toward 
the  nasal  side,  although  this  is  not  necessary  when  using  large 
wafers.  The  smaller  styles,  such  as  the  horseshoe  shape,  should 
be  cemented  in  this  way. 


The  Making  of  a  Mechanical  Optician  113 

CONCAVE  BIFOCALS 

In  making  concave  bifocals  the  wafers  should  be  cut  so  that 
the  thickest  part  is  upward  (Fig.  131).  This  is  to  neutralize  the 
prismatic  effect  of  the  distance  lens.  After  the  wafer  is  properly 
placed  and  the  lens  is  cool  (Fig.  132),  the  lower  edge  can  be  cut 
off,  using  a  pattern  the  shape  of  the  distance  lens.  It  is  then 
beveled,  if  for  frame,  and  ground  down  to  size;  if  for  frameless, 
it  is  ground  to  conform  to  the  shape  of  the  distance  lens  and 
beveled  slightly  to  take  ofif  the  sharp  edge. 

The  lens  should  then  be  cleaned  with  alcohol,  or  naphtha 
if  preferred.  If  it  is  then  found  that  the  cement  has  started, 
warm  the  lens  slightly  and  the  spots  will  probably  disappear. 

FRAMELESS  CEMENT  BIFOCALS 

In  n^.aking  frameless  cement  bifocals  it  is  a  good  plan  to 
drill  the  lenses  before  cleaning,  as  this  prevents  the  drilling  fluid 
working  under  the  wafer.  Wafers  should  always  be  fitted  to 
frameless  lenses  if  possible  before  drilling,  as  there  is  less  liability 
of  cracking. 

CEMENT  BIFOCALS 

The  grinding  and  cementing  of  a  bifocal  has  already  been 
described,  but  it  may  be  well  to  add  a  few  points.  Either  a 
composition  or  Craigleith  stone  can  be  used,  although  a  Craigleith 
is  preferable,  not  grinding  as  fast.  Wafers  should  be  very  thin, 
and  when  using  a  fast-cutting  stone  care  must  be  used  to  prevent 
them  grinding  away  too  fast,  and  thereby  producing  a  poor  shape. 
As  a  rule,  wafers  come  from  the  factory  with  very  clean  edges, 
but  even  if  they  are  more  or  less  irregular  it  is  unnecessary  to 
ctit  them,  unless,  of  course,  the  center  is  to  be  used. 

In  the  majority  of  cases  where  the  wafers  are  split  in  two 
before  grinding  there  is  very  little  difficulty  in  shaping  them  up. 
If  they  are  ground  separately  be  particular  to  see  that  the  shape 
is  uniform.  The  regulation  size  is  28  mm.  diameter  and  the 
height  is  varied  according  to  the  width  of  the  distance  lens,  al- 
though usually  from  13  to  14  mm.  high.  The  rule  is  to  set  the 
top  of  the  wafer  about  2  mm.  below  the  center  of  the  distance 
lens,  although  if  worn  constantly  a  lower  wafer  is  more  satis- 
factory.    This  depends  entirely  on  the  patient,  and  to  a  large 


114  T^^^  Making  of  a  Mechanical  Optician 

extent,  the  purpose  for  which  they  are  to  be  used.  For  example, 
a  bookkeeper  who  is  using  them  ahnost  constantly,  a  large  wafer 
may  be  preferred  (Fig.  133  ),  whereas  a  person  doing  very  little 
close  work  and  who  uses  them  only  occasionally  for  near  work, 
will  prefer  them  very  small  (Fig.  134). 

Wafers  can  be  obtained  from  the  jobbers  all  edged,  ready 
to  cement,  and  the  regular  size  is  2y  x  13.  To  obtain  this  size 
when  doing  your  own  grinding  it   is   necessary  to  grind  them 


Fig.    133  Fig.    134 

28  mm.  diameter,  as  before  stated,  for  the  reason,  when  cemented 
to  the  base  lens,  the  bottom  part  will  be  cut  off,  thereby  making 
them  smaller. 

The  principal  difficulty  the  beginner  finds,  after  he  has 
learned  to  cement,  of  course,  is  in  placing  the  wafer.  If  the  lens 
is  placed  on  the  bench  squarely  in  front  of  you,  after  it  has  been 
heated ;  or  in  other  words,  the  cement  has  boiled,  it  will  require 
some  few  seconds  to  cool.  During  this  period  there  is  plenty  of 
time  to  move  it  around  and  place  it  in  position.  After  training 
the  eye  it  will  soon  be  a  simple  matter  to  get  them  fairly  accurate, 
and  when  one  is  placed  just  where  you  want  it  you  will  then  have 
a  pattern  for  the  second  lens. 

If  after  allowing  it  to  cool  somewhat  you  find  when  laying 
one  over  the  other  they  do  not  match  exactly,  there  is  no  harm 
in  warming  one  or  the  other  slightly  and  moving  the  wafer  to 
the  proper  position.  It  is  a  very  simple  matter  to  get  the  wafers 
a  different  size  in  cementing  by  placing  one  higher  than  the  other, 
even  though  they  may  have  been  ground  alike.  One-half  a  milli- 
meter difference  is  very  noticeable  (see  Fig.  135).  This  cannot  be 
done  manv  times,  however,  as  either  the  cement  will  be  cooked 


The  Making  of  a  Mechanical  Optician 


115 


too  much  or  else  the  cement  will  be  squeezed  out  so  it  will  be 
too  thin.  In  this  case  bubbles  or  air  spots  are  very  likely  to 
appear  and  it  will  then  be  necessary  to  take  the  lens  apart  and 
start  all  over  again. 

When  the  lens  is  finished  and  a  bubble  or  base  spot  appears 
it  is  sometimes  possible  to  warm  the  lens  slightly,  and  this  will 


Fig.  135 

disappear.  It  should  first  be  tried  without  applying  any  pressure 
to  the  surface  of  the  wafer,  and  then  if  this  does  prove  successful 
it  will  do  no  harm  to  press  the  wafer  down  a  little.  It  must  be 
remembered,  however,  that  a  lens  should  be  heated  but  slightly ; 
in  other  words,  just  warmed.  For  this  work  the  regular  tweezers 
have  always  been  used,  but  recently  there  have  been  improve- 
ments made  which  are  quite  a  help.  Fig.  136  shows  an  improved 
tweezer,  which  holds  the  wafer  in  position  while  cementing;  it 
does  not,  however,  assist  the  workman  in  placing  the  wafer.  Fig. 
137  is  a  more  complicated  form,  which  can  be  termed  a  gauge. 


Fig.  136 


This  tool  is  constructed  so  that  the  jaws  can  be  spread  to  allow 
the  insertion  of  the  distance  lens.  This  can  be  set  squarely  so 
there  is  no  difficulty  in  placing  the  wafer  in  the  correct  position. 
By  the  use  of  the  scale  at  the  bottom  the  wafer  can  be  centered 
or  decentered  accurately.  All  wafers  should  be  decentered  in 
from  I  to  iy2  mm.  to  allow  for  convergence,  but  the  large  ma- 
jority are  placed  in  the  center.  The  lever  D  is  used  to  apply  the 
pressure  to  the  surface  of  the  wafer,  to  cause  the  bubbles  to 
disappear. 


ii6 


The  Making  of  a  Mechanical  Of'tician 


Electric  heaters  (Fig.  138)  are  now  used  to  a  great  extent  in 
bifocal  work,  as  the  heat  is  more  even  and  can  be  regulated  at 
will.     These  are  inexpensive  and  can  also  be  used  for  inserting 


Fig.  137 

lens  in  rubber,  zylonite  or  shell  lorgnettes,  as  well  as  eyeglasses 
and  spectacles.  This  heater  is  almost  indispensable  in  Opifex 
work. 

OPIFEX  BIFOCALS 

The  Opifex  bifocal  is  a  form  of  cement  bifocal,  which  has 
a  wafer  ground  extremely  thin  by  a  patented  process.     Where 


Fig.  138 

these  wafers  were  formerly  ground  only  by  prescription  shops 
licensed  by  the  patentee,  they  are  now  ground  by  the  American 
Optical  Company  and  the  Bausch  &  Lomb  Optical  Co.,  and  sup- 
plied the  same  as  stock  lenses.     These  are  ground  on  a  thick 


The  Making  of  a  Mechanical  Optician  n? 

"backing,"  so  that  they  can  be  edged  as  easily  as  any  lens,  or  if 
preferred,  they  are  suppHed  edged.  Figvire  139  illustrates  one  of 
these  wafers  in  the  rough,  although  the  edge  is  nearly  perfect, 
being  as  sharp  as  a  knife  edge  and  perfectly  round. 

These  wafers  can  be  edged  by  hand  fairly  well,  but  the  shape 
must  be  looked  after  very  carefully.  In  grinding  it  is  only  neces- 
sary to  grind  away  the  backing  and  simply  touch  the  edge  of  the 
wafer  as  slightly  as  possible.  This  will  clean  off  any  trace  of 
rouge  and  at  the  same  time  take  out  any  minute  chips.  Opticians 
who  have  edging  machines  will  find  it  to  their  advantage  to  have 
special  small  pads  made  to  accommodate  these  wafers  and  by 
grinding  them  by  machine  a  great  deal  of  time  will  be  saved,  and 
also  insure  a  perfectly  ground  wafer.  Figure  140  shows  the 
wafer  edged  and  ready  to  cement. 


Fig.   139  Fig.   140  Fig.    141 

Ikfore  cementing   it   will  be   necessary  to   ascertain   which 
surface  is  cemented  to  the  backing.*     In  some  cases  the  contact 
surface  will  be  upward,  and  in  others  it  will  be  cemented  to  the 
backing      For  this  reason  it  requires  two  different  methods  of 
handling      If  the  contact  surface  is  up  it  should  be  cleaned  and 
placed  on  the  heater  to  warm  it  slightly.     As  this  requires  but  a 
few  seconds  the  base  lens  can  be  cleaned  and  placed  on  the  heater 
at  the  same  time.     With  a  small  stick  or  a  pair  of  tweezers  the 
wafer  can  be  pushed  off  the  backing  slightly  (Fig.  141^  and  after 
the  cement  has  been  applied  to  the  base  lens,  grasp  the  backing 
and  turn  it  over  so  that  the  wafer  will  be  downwards  and  apply 
it  to  the  base  lens  (Fig.  142).     By  then  holding  the  wafer  with 
the  stick  the  backing  can  be  removed  and  the  wafer  then  placed 
in  position      With  the  electric  heater  this  operation  can  be  done 
entirely  on  the  iron  plate,  but  if  an  alcohol  lamp  is  used  care 
should  be  taken  not  to  heat  the  wafer  too  much  or  it  will  crack. 

"  '*The   Geneva   lens  measure,   constructed     especially     for     measuring 
wafers,   is   essential   to  measure  these  curves  accurately. 


Ii8  The  Making  of  a  Mechanical  Optician 

If  the  contact  surface  is  cemented  to  the  backing  it  is  un- 
necessary to  clean  it,  but  simply  start  the  wafer  from  the  block,  as 
before  described,  and  transfer  it  to  the  base  lens  without  turning  it 
over.  If  the  wafer  has  been  surface-ground  in  this  form  it  is  pos- 
sible to  bevel  the  edge  slightly  before  transferring  it,  but  this  is  not 
really  necessary.  It  must  not  be  done  if  the  contact  surface  is 
upward,  however,  as  the  bevel  will  be  on  the  wrong  side.  If  for 
any  reason  the  contact  surfaces  should  show  any  specks  of  dirt 
after  they  have  been  cemented,  the  wafer  can  be  transferred  to 


Fig.   142 

another  lens,  or  backing,  cementing  it,  of  course,  in  the  regular 
way.  It  does  not  matter  if  the  surfaces  do  not  fit,  as  the  cement 
will  have  body  enough  to  allow  the  contact  surface  to  be  cleaned. 
In  recementing  old  lenses  it  is  necessary  to  transfer  them  in  this 
manner,  to  clean  off  the  old  cement.  Be  sure  to  heat  the  lens 
sufficiently  so  the  wafer  is  moved  easily,  otherwise  when  starting 
it  the  wafer  will  crack  and  a  part  remain  on  the  base  lens. 

After  the  wafer  has  been  transferred  to  the  base  lens  it 
should  be  placed  in  position  and  cleaned  slightly.  It  will  then  be 
necessary  to  neutralize  the  reading  portion,  as  it  may  be  found 
wavy,  or  not  the  correct  focus.  It  must  be  remembered  these 
wafers  are  extremelv  thin,  consequently  are  easily  bent. 


The  Making  of  a  Mechanical  Optician  119 

As  it  is  necessary  to  hold  the  wafer  with  a  stick  when  sHding 
off  the  backing  it  is  not  unUkely  that  the  center  was  pressed  down, 
thereby  making  the  power  .12  to  .25  D.  weaker,  or  possibly 
wavy.  By  heating  the  lens  slightly  and,  if  necessary,  moving  it 
around  gently,  there  will  be  no  difficulty  in  producing  a  perfect 
lens.  Do  not,  under  any  circumstances,  attempt  to  make  these 
lenses  without  neutralizing  the  reading  portion  after  heating  each 
time.  This  also  applies  when  recementing  these  lenses,  and  if 
the  prescription  does  not  accompany  the  job  neutralize  them  be- 
fore removing  the  wafers  and  make  a  note  of  the  focus.  When 
the  wafers  are  in  the  correct  position  and  neutralized  correctly 
the  bottom  can  be  cut  off  and  edged  the  same  as  any  cement 
bifocal. 

In  cleaning  be  very  careful  not  to  chip  the  edges  and  when 
wiping  always  wipe  away  from  the  edge  of  the  wafer  and  not 
towards  it.  If  the  wafer  should  become  chipped  it  can  be  trans- 
ferred to  the  backing  and  ground  out.  Do  not  attempt  to  grind 
or  clean  the  wafer  when  not  on  the  backing,  as  this  is  practically 
impossible. 

Some  opticians  are  making  a  specialty  of  thin  wafers  ground 
the  shape  of  the  Opifex,  but  only  slightly  thinner  than  the  regular 
cement  bifocals.  Wafers  for  this  purpose  are  ground  small  in 
surfacing — usually  about  22  mm.  diameter.  They  are  then  edged 
to  18  mm.,  which  is  the  usual  size.  While  this  can  be  done  it  does 
not  produce  a  very  satisfactory  lens  and  at  the  same  time  requires 
more  time.  It  will  be  found  cheaper  in  the  end  to  purchase  the 
Opifex,  and  they  not  only  make  a  perfect  job,  but  are  much 
simpler  to  handle. 

For  Opifex  work  "cooked"  cement  will  be  found  more  con- 
venient and  it  also  simplifies  the  work  considerably.  When  the 
cement  has  been  prepared  so  that  it  requires  no  attention  it  is 
possible  to  do  better  work  on  the  lenses.  With  this  method  each 
job  is  cemented  alike,  and  if  the  cement  has  been  properly  pre- 
pared you  are  reasonably  sure  of  them  giving  satisfaction.  The 
method  of  preparing  cement  has  been  described  in  previous  ar- 
ticles. Occasionally  we  hear  of  substitutes  for  fir  balsam,  but 
as  yet  there  is  nothing  on  the  market  that  is  particularly  satis- 
factory.    All  of  these  preparations  adhere  to  the  surface  of  the 


I20  The  Making  of  a  Mechanical  Ol'tician 

lenses,  so  they  either  become  more  or  less  opaque  or  else  the 
wafers  cannot  be  removed. 

A  wafer  having  the  same  appearance  can  be  ground  from 
a  regular  wafer,  and  this  is  called  the  horseshoe  shape.  It  is 
no  more  invisible,  however,  on  account  of  the  thickness.  If 
special  wafers  are  ground  for  this  purpose  as  thin  as  possible, 
and  from  22  to  25  mm.  diameter,  it  is  possible  to  make  a  very 
fair  job.  The  prescription  houses  usually  charge  50  cents  extra 
over  the  regular  cement  price  for  these  lenses.  The  best  way 
to  handle  these  is  to  stick  them  to  the  end  of  a  stick,  about  the 
size  of  a  pencil,  with  sealing  wax.    They  should  be  edged  carefully 


Fig.    144 

to  iS  mm.  diameter.  They  are  then  cemented  to  the  distance 
lenses  in  the  regular  way,  but  so  that  the  top  will  be  2  mm. 
below  the  center  of  the  distance  (Fig.  143).  After  the  lenses 
are  cool,  the  bottom  is  cut  off  and  ground,  as  usual.  There  is  an 
occasional  call  for  round  wafers,  usually  about  10  mm.  diameter. 
These  can  be  ground  in  the  same  way,  but  cemented  to  the 
distance  about  2  mm.  from  the  lower  edge  (Fig.  144).  Oval 
wafers  are  also  ground  in  the  same  way. 

PERFECTION  BIFOCALS 

Perfection  bifocals  are  made  by  grading  out  the  lower  por- 
tion and  inserting  the  reading  lens.  The  distance  lens  is  first 
ground  to  size  and  the  lower  part  cut  with  a  hand  diamond  and  a 
round  pattern.  It  is  then  carefully  broken  out  and  ground  on  a 
small  alundum  stone.  These  stones  can  be  obtained  to  fit  any 
buff  head   and   in  any  size.     The  regulation   shape   is  one   inch 


The  Making  of  a  Mechanical  Optician  121 

diameter,  although  occasionally,  when  a  larger  lower  is  desired, 
1 14  inch  is  used.  The  lower  lens  is  then  cut  the  same  shape  and 
ground  on  the  regular  stone  to  fit  this  curve.  Although  these 
can  be  ground  into  the  frames  separately,  it  is  better  to  stick 
them  together  with  white  sealing  wax.  If  this  method  is  used, 
the  wax  must  be  left  in  (and  this  is  no  objection).  If  cleaned 
out  the  lens  will  be  too  small  for  the  frame. 

Grooved  Perfection  bifocals  have  been  used  to  some  extent 
and  the  advantage  claimed  is  that  the  parts  are  interchangeable 
and  can  be  made  up  from  stock  very  quickly.  The  line  between 
the  distance  and  reading  is  quite  conspicuous,  however,  and  for 
this  reason  they  have  never  had  a  large  sale,  especially  since  the 
demand  for  invisible  bifocals. 

The  distance  lenses  can  be  ground  the  same  as  the  regular 
Perfection,  except  that  the  curve  is  beveled  instead  of  flat.  This 
can  be  done  on  the  small  stone  without  any  difficulty.  The  lower 
part  is  then  ground  flat  to  fit  the  curve  of  the  upper  and  a  groove 
made  with  a  rat  tail  file  and  drilling  fluid. 

Perfection  bifocals  are  rarely  used  except  in  cases  where  a 
patient  is  obliged  to  work  near  heat  and  cannot  afiford  the  fused 
lenses.     It  is  also  impractical  to  make  them  in  frameless. 

SPLIT  BIFOCALS 

Split  bifocals  can  be  centered  or  not  as  you  prefer.  Or- 
dinarily they  are  not,  and  when  ground  in  this  way  the  four  pieces 
can  be  cut  from  two  lenses,  providing  the  power  is  the  same  in 
both  eyes.  The  lenses  are  first  split  in  the  center  and  the  straight 
edges  ground  on  the  side  of  the  stone.  Composition  stones  are 
molded  and  the  sides  are  usually  smooth  enough.  If  not,  the 
right  side  should  be  honed  the  same  as  the  face.  If  a  Craigleith 
is  used  the  side  will  have  to  be  turned  true  with  a  diamond  and 
boned  with  a  piece  of  Craigleith.  When  the  straight  edges  are 
ground  and  beveled  slightly  to  take  ofif  the  sharp  edge,  they 
should  be  stuck  together  with  white  sealing  wax.  They  can 
then  be  handled  as  one  lens  and  cut  to  size  with  a  pattern.  They 
are  also  ground  the  same  as  any  lens.  These  lenses  can  also  be 
ground  separately  if  desired,  but  it  is  more  difficult  to  hold  them 
when  trying  in  the  frame.     If  centered  lenses  are  required  the 


122  The  Making  of  a  Mechanical  Optician 

halves  should  be  cut  from  the  center  of  the  lens  and  a  pattern 
having  this  shape  will  be  required. 

Whole  bifocals  are  surface  ground  and  are  treated  the  same 
as  an  ordinary  lens  when  ground  to  size.  These  are  not  recom- 
mended on  account  of  the  prismatic  effect. 

FUSED  BIFOCALS 

Fused  bifocals  are  a  surface-grinding  proposition  and  will 
be  described  under  that  heading  later.  The  blanks  can  be  obtained 
and  if  care  is  used  it  is  not  difficult  to  surface  them.  At  present, 
however,  we  will  suppose  that  you  prefer  to  buy  them  uncut  and 
edge  them  yourself.  When  ordering  them  from  the  jobbers, 
full  information  must  be  given,  such  as  distance  and  reading 
powers,  diameter  and  height  of  reading  portion,  axis,  frame  or 
frameless,  if  reading  part  is  to  be  set  in  and  size  of  eye.  When 
the  lenses  are  received  the  axis  should  be  marked  and  a  cutting 
line  drawn.  The  reading  portion  is  then  dotted  with  ink  around 
the  edge  so  that  the  circle  can  be  seen  easily.  The  usual  diameter 
is  i8  mm.,  and  the  height  is  within  2  mm.  of  the  center.  After 
the  axis  and  position  of  the  disk  is  inspected  the  lens  is  cut  by 
pattern.  Although  these  lenses  can  be  edged  by  machine,  it  is 
recommended  that  they  be  ground  by  hand.  The  position  of  the 
disks  can  then  be  watched  and  there  will  be  less  liability  of  spoiling 
them.  Also  be  particular  that  the  disk  is  not  scratched  as  flint 
is  much  softer  than  crown  glass.  In  edging  these  lenses  the  disks 
should  be  first  considered ;  that  is,  the  shaping  of  the  lens  should 
be  done  on  the  lower  edge  first  to  make  the  disks  the  same  height. 
After  these  have  been  made  just  right,  proceed  to  shape  up  the 
other  part  of  the  lenses.  In  making  the  various  combinations 
it  is  necessary  to  use  flint  of  different  indices  and  some  of  these 
grind  quite  hard.  For  these  lenses  Craigleith  stones  will  be 
found  more  satisfactory. 


CHAPTER  XI 


BRIDGE  BENDING  AND  TRUING 

Bridges  can  be  bent  before  or  after  mounting,  and,  although 
there  is  really  no  preference,  some  opticians  obtain  better  results 
one  way  and  some  another.  When  bending  an  unmounted  frame- 
less  bridge,  or  a  frame  before  the  lenses  are  inserted,  gripping 
pliers  can  be  used  to  hold  the  strap  or  eye  wire  so  that  the  opera- 
tion is  simplified.  An  experienced  person,  however,  can  bend 
just  as  well  after  mounting,  but  the  bridge  must  be  held  in  the 
fingers.  Under  no  circumstances  should  the  spectacles  be  held 
by  the  lenses  as  they  will  surely  be  broken. 

Bridge  bending  is  not  hard  to  learn,  but  simply  requires 
practice  and  a  good  eye.  It  is  discouraging  at  the  first  attempt, 
and  the  reason  is  that  the  beginner  starts  to  bend  some  frame  to 
certain  dimensions,  probably  selecting  a  difficult  one,  and  possibly 
one  that  could  not  be  bent  successfully  anyway.  In  starting 
this  work,  select  some  old  frames  of  soft  metal,  such  as  German 
silver  or  Roman  alloy,  as  these  make  the  best  frames  to  practice 
on,  and  always  have  some  dimension  to  work  to,  as  nothing  can 
be  accomplished  by  bending  at  random. 

For  the  first  operation  take  a  frame,  say  60  mm.  P.  D.,  and 
bend  it  to  58.  This  is  done  by  holding  the  bridge  with  a  pair  of 
No.  36  pliers  in  the  left  hand  and  gripping  the  shank  of  the 
bridge  with  a  pair  of  round  or  snipe-nose  pliers  about  half  way 
from  the  eye  wire  to  the  turn,  and,  with  a  slight  twist  to  the 
right,  the  eye  is  bent  toward  you  (Fig.  145).  Then  grasp  the 
shank  near  the  eye  wire  and  bend  the  eye  back,  and  you  find  that 
the  shank  has  the  desired  bend  and  the  eye  has  been  thrown  in 
quite  a  little.    The  amount,  of  course,  depends  on  the  twist. 

After  bending  this  to  the  required  P.  D.,  bend  it  back  again 
to  the  original  shape.  This  will  give  you  practice  in  widening 
the  P.  D.  This  is  accomplished  by  straightening  the  shank  with 
a  pair  of  snipe-nose  pliers ;  in  other  words,  take  out  the  curve 
known  as  the  47  style.  In  this  operation  the  eye  is  thrown  for- 
ward and  it  should  then  be  brought  into  line  with  the  No.  36  pliers. 


124 


The  Making  of  a  Mechanical  Optician 


A  frameless  bridge  is  bent  the  same  way,  except  that  it  is 
necessary  to  have  different  pHers  to  hold  the  strap,  and  for  this 
purpose  the  No.  39  anghiig  phers  are  the  best  (Fig.  146). 

Next  try  raising  and  lowering  the  bridge.  This  is  done  by 
holding  the  eye-wire  with  the  Ko.  36  pliers  or  the  snipe-nose  in 


Fig.    146 


the  right  hand  and,  grasping  the  crest  of  the  bridge  with  the 
thumb  and  forefinger  of  the  left  hand,  bending  it  up  or  down. 
This,  of  course,  changes  the  angle  of  the  crest  a  little,  also  the 
inset  or  outset,  still  it  is  the  first  step  necessary  (see  Fig.  147). 

If  vou   desire  to  lower  the  bridge  and  keep  the  angle  the 
same,  bend  the  bridge  down,  as  described  in  Fig.  40,  then  grasp 


Fig.    147 


Fig.    148 


the  frame  with  the  No.  36  pliers  (if  frameless.  the  No.  39  pliers) 
in  the  right,  and  the  shank  of  the  bridge  with  a  flat-nose  pliers 
in  the  left  hand,  bend  the  shanks  downward  (see  Fig.  148).  It 
is  impossible  to  raise  the  bridge  and  keep  the  angle  of  the  crest 
and  the  inset  or  outset  the  same,  except  by  shortening  the  shanks, 
and  this  should  not  be  attempted  until  the  first  operations  are 
mastered. 


The  Making  of  a  Mcclwuical  Optician  125 

To  widen  the  base  take  a  pair  of  flat,  or  snipe-nose  pliers, 
and  place  a  piece  of  cloth  between  the  jaws  to  prevent  marring 
the  bridge,  and  flatten  it  to  the  required  measurements  and  shape ; 
then  straighten  the  frame  and  you  will  find  that  the  bridge  is 
right,  but  the  P.  D.  is  wide.  The  shank  can  then  be  bent,  as 
explained  before,  to  shorten  the  P.  D. 

To  increase  the  outset  it  is  necessary  to  shorten  the  shanks, 
and  it  is  quite  difficult  to  do  this  without  marring  the  stock,  but 
if  you  go  slow,  bending  a  little  at  a  time,  this  can  be  done  all 
right.  The  first  operation  is  to  grasp  the  bridge  with  the  thumb 
and  forefinger  of  the  left  hand  and,  with  a  pair  of  round  pliers 
in  the  right  hand,  gradually  open  up  the  turn,  beginning  with  the 


Fig.   149 

small  end  of  the  pliers  and  gradually  sliding  the  bridge  toward 
the  larger  part  of  the  pliers  (see  Fig.  149)-  After  this  has  been 
spread  sufficiently,  grasp  the  shank  a  little  way  from  the  turn 
and  bend  the  eye  straight,  at  the  same  time  pulling  forward  on 
the  bridge  with  the  left  hand.  This  pulls  a  little  of  the  stock  in 
the  shank  into  the  arch.  It  can  then  be  trued  up  and  the 
operation  repeated  on  the  left  side. 

To  decrease  the  outset  or  increase  the  inset  the  shank 
must  be  lengthened  and  the  first  operation  is  to  open  the  turn 
of  the  shank  a  little,  as  before,  but,  instead  of  grasping  the 
shank  back  from  the  turn,  grasp  it  near  the  turn,  or,  if  possible, 
in  the  turn,  bend  the  eye  straight  and  true  up.  Repeat  the  opera- 
tion on  the  left  side. 

After  practicing  with  the  sample  frame  select  a  good  frame 


126  The  Making  of  a  Mechanical  0(^ticiaii 

to  bend  to  measurements.  The  principal  part  of  selecting  frames 
for  prescription  jobs  is  in  using  good  judgment,  and  you  should 
train  yourself  to  judge  whether  a  frame  can  be  bent  to  the 
dimensions  required  or  not.  If  you  do  not  learn  this  you  can 
never  learn  to  bend  and  will  spoil  stock,  also  waste  time.     In 


Fig.  150 

selecting  a  frame  try  and  get  everything  right  but  one  dimension, 
if  possible,  and  it  is  best  to  change  the  P.  D.,  as  this  is  easier 
than  anything  else.  Do  not  take  up  a  frame  at  random  and 
expect  to  bend  it  to  fit  the  required  dimensions,  but  study  it 
carefully  and  learn  to  judge  it  before  touching  it  with  the  pliers. 

After  the  lenses  are  mounted  they  must  be  trued  up,  and, 
if  the  bridge  has  been  bent  previously,  it  is  a  very  simple 
operation.  If  it  has  not  been  bent  it  is  best  to  straighten  it 
somewhat  and  lay  it  on  the  pupilometer  to  get  an  idea  of  what 
is  to  be  done.  The  first  operation  is  to  get  the  lenses  in  the 
same  plane,  so  that  they  will  lie  flat.  Then  turn  the  spectacles 
over,  holding  them  endwise  and  sight  across  the  outside  surfaces. 
The  four  glass  screws  should  then  be  brought  into  line  (Fig.  150). 
The  spectacles  should  then  be  measured  for  all  dimensions  and 
any  necessary  alterations  made  at  this  point. 

We  now  suppose  that  the  front  is  correct  and  true,  and  the 
attention  turned  to  the  temples.  First  straighten  and  true  them 
so  that  the  curve  will  be  uniform.  Then  hold  the  front  endwise 
with  the  temples  upward,  and  in  almost  every  case  they  will  be 
found  with  one  angled  one  way  and  the  other  in  the  opposite 
direction  (Fig.  151).  A  pair  of  parallel  jaw  pliers  (No.  40) 
should  then  be  used  to  grip  the  endpiece  close  to  the  strap  or 
eye-wire,  and,  with  a  pair  of  snipe-nose  pliers,  the  joint  is  angled 
to  make  the  temple  perpendicular    (Fig.    152).     The  temple  is 


Tlie  Making  of  a  Mechanical  Optician  127 

then  shut  down,  and,  if  it  is  not  in  line  with  the  endpieces,  it  is 
turned  to  the  right  or  left,  both  pliers  being  used  in  the  same 
position.  This  operation  is  then  repeated  on  the  other  joint. 
If  the  front  is  to  be  angular,  the  joints  are  tilted  in  the  same 
manner. 

Should  it  be  necessary  to  set  the  temples  back,  the  tip  can 
be  filed  at  the  joint  if  gold  or  steel,  but  in  gold  filled  it  is  better 
to  hold  the  joint  with  a  pair  of  pliers  and  pull  the  temple  outward 
with  the  fingers.  Although  one  may  be  broken  occasionally,  it 
saves  filing  the  gold,  which  is  very  important  when  handling 
filled  goods.  There  are  no  pliers  on  the  market  for  holding  the 
endpiece  in  this  operation,  but  they  can  be  made  specially  for 
any  make  or  style  of  joint. 

In  truing  eyeglasses  there  is  very  little  to  be  done  except 
to  straighten  the  lenses  so  that  they  are  in  the  same  plane,  and 
adjust  them  so  that  the  droop  will  be  right.  This  is  a  very 
important  feature  and  many  opticians  do  not  understand  that  an 
eyeglass  should  be  placed  as  far  back  on  the  nose  as  possible.  A 
great  many  times  a  patient  requests  that  the  spring  be  tightened, 
when  in  reality  it  should  be  opened  more  to  allow  the  guards  to 


Fig.  151 

go  back  farther.  Each  time  the  spring  is  tightened  the  glasses 
are  thrown  farther  forward  and,  finally,  they  will  grip  only  on 
the  very  edge.  Now,  in  truing,  the  lenses  are  allowed  to  droop 
a  little  so  that  when  placed  on  the  nose  they  will  be  horizontal. 
If  they  were  in  this  position  before  placed  on  the  face,  or  if  the 
guards  are  not  spread  enough,  the  lenses  will  set  upward.    This 


128  The  Making  of  a  Mechanical  Optician 

not  only  looks  badly  but  the  lenses  will  be  too  high.  A  great 
many  times  eyeglasses  are  sent  to  the  prescription  houses  for 
drop  studs  or  guards  to  set  the  lenses  lower,  or  even  for  new 
lenses  drilled  above  center,  when  all  that  is  necessary  to  make  the 
glasses  right  is  to  droop  the  lenses  a  little  more. 

When  lenses  are  drilled  above  center  they  must  always  be 
turned  down.  For  this  operation  grasp  the  stud  with  a  pair 
of  stud  pliers  in  the  right  hand  and  hold  the  spring  with  tlie  left. 
By  bending  the  spring  away  from  the  lenses  it  will  give  them 
the  required  droop.    Then  take  hold  of  the  studs  with  both  hands 


Fig.  152 

and  open  the  spring  a  little  until  the  lenses  appear  to  be  in  about 
the  right  position.  The  guards  should  then  be  adjusted  so  they 
are  parallel. 

For  truing  a  fingerpiece  mounting  use  the  No.  40  pliers, 
placing  the  jaw  marked  "top"  with  the  large  hole  over  the  head 
of  the  screw  on  which  the  spring  is  coiled.  The  lenses  can  then 
be    changed    to    any    position    without    damaging   the    mounting 

(Fig-  153)- 

When  it  becomes  necessary  to  drop  the  lenses  in  an  eyeglass 

frame  to  make  them  lower  on  the   face,  the   screws  should  be 

loosened  in  the  end-pieces  and  the  lenses  twisted  so  that  they  set 

upward  considerably.     Then  grasp  the  studs  with  the  stud  pliers 

in  the  same  manner  as  before  described  for  frameless,  and  twist 

the  eye  downward,  etc.     If  the  lenses  need  to  be   raised,  they 


I'lie  Making  of  a  Mechanical  Optician 


129 


should  be  twisted  downward  in  the  frames,  the  studs  grasped 
with  the  stud  pHers,  and  the  spring  bent  backward  toward  the 
lenses,  thereby  raising  the  eye  to  the  required  position.  This  is 
another  case  that  occurs  frequently  in  prescription  work  where 


Fig.  153 

frames  are  ordered  with  studs  above  center.  If  the  lenses  are 
fitted,  they  can  be  adjusted  easily  and  no  explanation  is  required; 
but  if  the  frames  only  are  ordered,  it  is  almost  impossible  to  shape 
them  so  that  they  look  right,  and,  even  if  this  is  possible,  the 
optician  can  easily  change  the  position  in  fitting  them  up. 

Toric  lenses  can  be  adjusted  so  that  they  curve  slightly  to 
conform  to  the  features.  If  there  is  too  much  curve,  however, 
it  may  be  objectionable  to  the  patient.  It  is  well  to  remember 
this  point,  as   frequently  people  complain  that  they  are  unable 


Fig.  154 


to  wear  torics,  and,  if  the  glasses  are  adjusted  so  that  the  angle 
is  changed,  it  makes  them  entirely  satisfactory. 

This  also  applies  to  the  angle  for  reading,  but  not  so  much 
with  torics  as  flat  lenses.  According  to  theory  all  glasses  should 
be  angled  slightly,  and  the  amount  depends  somewhat  on  the 
features. 


130  The  Making  of  a  Mechanical  Optician 

Lenses  should  never  be  drilled  below  center.  If  the  spectacles 
are  too  low  on  the  face,  the  bridge  can  be  altered  to  raise  them 
even  if  it  is  necessary  to  make  one  to  order.  It  is  seldom  that  a 
regular  bridge  cannot  be  used  by  dropping  the  shanks. 

If  eyeglasses  are  too  low  they  should  be  raised  by  changing 
the  guards  to  some  other  style.  In  many  cases  a  regular  offset 
guard  with  a  short  blade  will  accomplish  this  result.  It  should 
be  remembered  that  to  raise  the  lenses  the  guard  should  be  lower, 
and  to  lower  the  lenses  the  guards  should  be  higher. 

There  are  so  many  guards  on  the  market  that  it  is  well  to 
look  the  common  styles  over,  and  it  will  be  noticed  that  the  arms 
are  set  very  differently  on  different  styles.  If  one  is  familiar 
with  these  styles  it  is  a  very  easy  matter  to  select  a  different  one 
to  accomplish  whatever  result  is  required.  When  there  is  diffi- 
culty in  fitting  glasses  so  that  they  will  be  low  enough,  the  drop 
eye  lenses  sometimes  are  a  great  help,  especially  when  the  eyes 
are  deep  set. 

In  truing  temples  do  not  leave  too  much  curve  to  them,  but 
have  them  so  that  they  will  be  straight  to  the  turn  so  that  all  the 
curve  will  be  behind  the  ear.  The  right  way  to  fit  a  temple  is 
to  make  quite  a  sharp  turn  at  ear  (Fig.  154).  These  not  only 
prove  more  comfortable  but  they  look  better.  When  the  nose  is 
sensitive,  cylinder  bridges,  cork  or  shell  nose  guards  can  be  used, 
but  when  fitting  the  latter  the  bridge  must  be  somewhat  higher  to 
allow  for  the  thickness  of  the  cork  or  shell. 


CHAPTER  XII 


SURFACE  GRINDING 

Surface  grinding  is,  in  reality,  a  separate  branch  of  me- 
chanical optics,  for  the  reason  that  few  opticians  doing  their 
own  work  attempt  to  do  this  work.  Usually  an  optician  puts  in 
a  plant  to  do  his  own  edging,  and  for  this  part  of  the  work  he 
has  time  enough,  but  it  is  not  practical  to  attempt  to  surface 
the  few  odd  combinations  that  he  may  be  called  upon  to  supply 
and  attend  to  his  trade  at  the  same  time.  The  right  way  is  to 
install  the  outfit  for  edging,  and,  as  his  work  increases,  he  can 
afford  to  hire  a  man  for  this  part  of  the  business.  He  can  then 
install  the  surface  plant  for  the  accommodation  of  his  customers 
or  for  the  advertising  feature. 

It  requires  verv  little  time  to  grind  an  ordinary  lens  if  the 
workman  is  efficient,  and  it  often  saves  a  delay  of  twenty-four 
to  thirty-six  hours  if  it  is  necessary  to  send  out  of  town  to  a  jobber. 
A  surface  machine  can  be  obtained  for  $58.50  and  upward. 
The  simple  machines  have  one  speed,  and  although  this  is  suffi- 
cient it  is  often  convenient  to  have  two  speeds  (Fig.  I55>-  ^^ 
one  speed  only  is  used,  900  to  1200  revolutions  per  minute  are 
most  satisfactory.    If  two  speeds  are  used,  600  and  1200  are  the 

most  common. 

A  lens  can  be  ground  using  almost  any  speed,  but,  of  course, 
the  higher  the  speed  the  faster  the  grinding,  although  it  requires 
more  attention  as  it  is  also  necessary  to  feed  the  emery  faster. 
There  is  a  limit  as  to  speed,  however;  if  it  runs  too  fast  it  throws 
the  emery  oflf  quickly  and  you  then  are  grinding  on  the  tool,  and 
in  this  way  nothing  is  accomplished.  It  must  be  remembered 
that  it  is  the  emery  that  grinds  and  not  the  tool. 

The  electrical-driven  machine  is  very  convenient  as  the  motor 
is  enclosed  in  the  base,  and,  consequently,  does  not  require 
countershafts  or  belts  (Fig.  15'V).  It  also  not  only  requires  very 
little  power  to  operate  it,  but  when  the  machine  is  stopped  it  is 
using  no  current.  These  machines  can  be  obtained  in  direct 
current  only  at  present.  There  are  also  automatic  surface  ma- 
chines on  the  market,  and  these  can  be  used  either  by  hand  or 


131 


132 


The  Making  of  a  Mechanical  Of'tician 


not  as  you  choose  (Fig.  157).  Automatic  work  is  somewliat 
slower,  and  most  opticians  having  these  machines  use  this  attach- 
ment for  polishing  only. 

The  tools  cost  about  two  dollars  per  pair  and  the  gages  about 


seventy-five  cents  per  pair.  These  are  not  supplied  with  llie 
machine,  so  it  is  necessary  to  order  whatever  powers  will  be 
needed.  It  is  well  to  have  each  .12  to  3  D.,  then  .25  to  8  D.,  then 
.30  to  14  D.,  and  each  diopter  to  20  D. ;  also  a  piano  and  an 
extra  6  D.  for  roughing  torics.  It  is  also  necessary  to  have  a 
pair  of  gages  for  each  power. 

Another  point  that  must  be  considered  is  whether  B.  &  L. 
or  A.  O.  Co.  glass  will  be  used.  If  both,  it  will  be  necessary  to 
have  a  set  of  tools  for  each,  although  by  making  an  allowance 
it  is  possible  to  work  very  closely  on  one  set  of  tools.  There  is 
about  .03  D.  difTerence  on  each  diopter,  and,  as  this  is  so  small, 
it  will  come  near  enough  up  to  2  D.,  but  above  that  select  the 
nearest  tool  and  polish  it  stronger  or  weaker  as  the  case  requires. 
(This  will  be  explained  later.) 


The  Making  of  a  Mechanical  Optician 


133 


The  index  of  A.  O.  Co.  glass  is  1.507  and  B.  &  L.  1.522. 
To  obtain  the  required  radius  multiply  the  focus  wanted  in  inches 
by  the  index  of  refraction,  —  i.  For  example,  i  D.  is  39.37 
inches  and  the  index  of  B.  &  L.  glass  is  1.522.  We  would  then 
multiply  39.37  by  .522,  which  would  make  the  radius  of  the 
tool  for  I  D.  20.55  inches.  This  does  not  enter  into  the  work  in 
any  way,  however,  unless  the  optician  is  mechanically  inclined 
and  he  desires  to  make  his  own  tools.  It  is  simply  necessary, 
when  ordering  tools,  to  state  what  glass  they  are  to  be  used  for. 

For  grinding  material  the  following  grades  of  emery  will 
be  required :  No.  60  for  roughing.  No.  100  for  smoothing,  No.  4-F 
for  finishing  and  a  grade  of  washed  emery  for  fine  finishing. 
The  first  three  mentioned  should  be  bought  in  ten-pound  cans ; 
the  washed  can  only  be  obtained  from  optical  concerns  in  five- 


Fig.  156 


pound  cans.  This  is  also  very  expensive,  as  compared  with  other 
grades,  but  it  lasts  a  long  time  as  it  is  necessary  to  use  only  a 
very  small  quantity  at  a  time.  It  should  also  be  remembered 
that  a  good  finish  saves  a  great  deal  of  time  in  polishing. 

There  are  several  kinds  of  grinding  material  on  the  market. 


134 


The  Making  of  a  Mechaiiical  Optician 


such  as  carborundum,  corundum,  alundum  and  crushed  steel,  and 
these  are  graded  about  the  same  as  emery.  They  cost  more,  but 
are  supposed  to  cut  faster  and  stay  sharp  longer,  but  for  a  single 
machine  it  hardly  pays  to  mix  the  different  materials.     It  should 


Fig.  157 


be  remembered  that  the  sharper  or  rougher  the  materials  used 
the  harder  it  is  on  the  tools  and  they  must  be  watched  more 
carefully  to  see  that  they  are  kept  true.  For  polishing,  rouge  is 
used,  and  this  comes  in  several  grades.  The  grade  used  by 
jobbers  is  all  right  and  should  be  ordered  in  five-pound  boxes. 
There  is  also  a  black  pigment  used  by  some  opticians.  For  polish- 
ing, cloth,  felt  or  broadcloth  is  most  commonly  used,  and,  although 
this  can  be  obtained  almost  everywhere,  it  is  more  satisfactory 
to  order  it  from  the  jobber  and  you  will  then  be  sure  of  getting 
a  quality  that  will  do  satisfactory  work.  Pitch  can  be  obtained 
in  one-pound  cans  from  the  jobbers,  and  this  is  used  to  stick  the 
lenses  on  to  the  blocks.  It  can  be  made  easily  by  taking  a  quantity 
of  resin  and  melting  it.  When  it  is  poured  oft'  to  cool,  a  little 
turpentine  should  be  added  to  soften  it,  or,  in  other  words,  to 
keep  it  from  getting  brittle.  In  the  winter  it  should  be  softer 
than  in  the  summer,  as  the  temperature  will  affect  it.  If  it  is  too 
soft  the  glass  will  slide  on  the  block  in  polishing,  and  if  too  hard 
it  will  jump  off  the  block  when  chilled  in  water.  To  make  it 
black  a  little  lampblack  can  be  added.  The  dark  surface  makes 
it  much  easier  to  inspect  the  lenses  when  polishing. 


The  Making  of  a  Mechanical  Optician  I35 

A  few  blocks  are  usually  furnished  with  a  machine,  but  more 
will  be  required.    Those  furnished  are  round  and  flat  (Fig.  I5«), 
and  these  will  do  for  weak  power  lenses.     For  stronger  powers 
deeper  holes  are  needed,  so  they  are  made  with  a  lug  on  the  back 
(  Fi-   I  w  )      Some  of  these  should  have  a  convex  face  ( t  ig.  ibo  ) 
and'some  concave  for  torics   (Fig.   i6i).     If  square  blocks  are 
used  it  will  be  much  easier  to  caliper  the  lens  while  grinding.     A 
few  small,  round  blocks  wiU  also  be  needed  for  wafers  (Fig.  162). 
Before  fitting  the  tool  to  the  machine  it  should  be  tried 
with  the  gage,  and  if  it  is  not  perfectly  true  it  should  be  made 
so  before  attempting  to  grind  the  lens,  otherwise  the  power  will 
not  be  correct     'A  great  many  opticians  use  tools  without  gages, 
or   even  if  thev  do  have  them,  they  allow  the  tools  to  get  all  out 
of'  true  and  then  send  them  to  a  machinist  to  be  put  in  shape. 
This  is  entirely  wrong  and  unnecessary,  as  it  is  a  very  easy  matter 
to  true  the  tool  a  little  each  time.     The  method  is  the  same  as 
trying  the  surface  of  a  board  to  see  if  it  is  square;  that  is,  the 
tool  is  held  in  one  hand  on  a  level  with  the  eye  and  the  gage  is 
held  perpendicular  to  the  surface.     If  no  light  can  be  seen  it  will 
fit  perfectly;  if  light  is  seen,  notice  whether   it   is  weaker  or 
stronger  or  if  there  is  simply  a  high  or  low  spot.     In  grmdmg, 
usually  the  tool  wears  on  the  side  and  the  center  will  be  high 
For  this  work  a  piece  of  carborundum  8  in.  long,  2  in.  wide  and 
I  in    thick  is  used  of  a  fairly  coarse  grade.     The  tool  is  placed 
on  the  spindle  and  run  at  full  speed.     With  the  carborundum 
stick  it  can  be   turned   nearly   as   well   as   in   a   lathe.     A  htt  e 
should  be   taken   ofT  at   a   time,   however,   and   tried    frequently 
with  the  gage. 

There  are  usually  two  pans  furnished  with  the  machine; 
one  of  these  should  be  used  for  grinding  and  the  other  for 
polishing.  Some  rough  emery  (No.  60)  is  placed  in  the  pan  with 
quite  a  lot  of  water,  enough  so  that  it  covers  the  emery.  It  will 
do  no  harm  if  there  is  too  much  as  the  emery  will  stay  at  the 
bottom  In  roughing,  this  is  fed  on  to  the  tool  with  a  spoon  or 
with  the  fingers.  The  No.  100  emery  should  be  placed  in  an  agate 
drinking  cup,  or  something  of  that  nature,  and  wet  so  that  it 
will  be  in  the  form  of  a  paste.  The  No.  4-F  emery  can  also 
be  placed  in  a  cup  of  this  kind,  but  the  washed  should  be  kept 
in  a  small  jar  or  box  with  a  cover.     The  rouge  can  be  placed 


136 


The  Making  of  a  Mechanical  Ol^ti. 


cian 


in  a  cup  and  wet  in  the  same  way.  An  extra  cup  of  water  should 
be  kept  at  side  of  this,  and,  in  polishing,  this  is  apphed  with  a 
brush.  It  will  be  necessary  to  have  a  large  pail  of  water  handy 
for  rinsing  the  lens  from  time  to  time,  and,  after  these  different 
receptacles  are  arranged  conveniently,  you  will  be  ready  to  grind. 
For   surface   grinding   it    is   necessary   to   have   a   stock   of 


-N 7- 


Fig.   158 

rough  cylinders.  These  come  in  thickness  varying  from  2  to  lo  mm. 
Those  most  commonly  used  are  2)4  and  4  mm.  In  selecting 
the  stock  for  any  particular  job  it  is  well  to  caliper  them,  as  this 
not  only  saves  glass,  but  also  saves  a  great  deal  of  time  in  rough- 
ing.    For  this  work  a  pair  of  calipers  graduated  in  1/5  mm.  is 


T 7- 

\     / 


^  Fig.   159 

used  (Fig.  ifij'-  ^t  is  necessary  to  allow  2/5  mm.  for  each 
diopter  and  4/5  mm.  for  each  prism  diopter.  To  this  is  added 
about  2/5  mm.  for  grinding.  For  example,  if  we  are  to  grind 
-(-  I  ==  -|-  .50,  a  -f-  .50  cylinder  is  selected  4/5  mm.  thicker  on 
the  edge  than  the  required  thickness  of  the  finished  lens,  thus 


-r 


V 


Fig.   160 


allowing  2/5  mm.  for  the  curve  and  2/5  mm.  for  the  grinding. 
When  grinding  a  convex  lens  the  center  is  hardly  touched,  pro- 
viding the  stock  is  about  the  right  thickness  at  the  start,  but, 
unless  the  lens  is  fined  down  very  carefully,  which  takes  extra 
time,  you  cannot  help  grinding  off  a  little  extra  glass,  and,  for 
this  reason,  a  little  allowance   for  grinding  must  be  made.     If 


The  Making  of  a  Mechanical  Optician  I37 

the  combination  to  be  ground  were  —  i  =  —  .50,  a  rough  cyhnder 
having  about  the  right  thickness  on  the  edge  would  be  selected 
as  practically  the  center  only  is  ground.  The  allowance  for  grind- 
ing is  all  that  would  be  taken  off  the  edge.  If  the  combination 
to\e  ground  were  +  i  =  +  .50  axis  90  =  1°  in,  it  would  be 
necessary  to  allow  4/5  mm.  more  for  the  prisms.  For  example, 
the  lens  when  finished  should  be  2  mm.  thickness  on  the  edge; 
to  this  is  added  2/5  mm.  for  the  one  diopter  and  4/5  mm.  for 
the  prism.  To  this  is  added  2/5  for  grinding  and  the  rough 
cylinder  to  be  selected  would  be  3  3/5  mm.  For  this  it  would 
probably  be  necessary  to  use  4  mm.  stock.     It  should  be  remem- 


■'^ Z" 


[^=^ 


Fig.   161 

bered    that    over   4   mm.    rough    cylinders    cost    extra    for    each 
millimeter  thickness. 

Toric  rough  cylinders  should  be  purchased  in  molded  form, 
when  possible,  as  this  saves  a  great  deal  of  roughing.  Most^all 
blanks  are  made  this  way  at  the  present  time,  but  some  of  the 
smaller  manufacturers  put  them  out  in  flat  form.     There  is  also 

I     ^      I 

Fig.  162 

another  point  to  be  considered  in  using  these  lenses,  and  that  is 
that  often  it  is  not  possible  to  get  the  thickness  out.  In  other 
words,  when  they  are  not  molded,  so  much  stock  has  to  be  ground 
out  inside  that  it  leaves  the  lens  a  knife  edge.  These  can  be 
obtained  in  plus  and  minus  6  D.  base  curve,  also  plus  and  minus 
9  D.  base  curve.  The  majority  of  combinations  can  be  ground 
on  +  6  D.  base,  but,  as  the  spherical  power  increases,  it  reduces 
the  toric  effect  so  that  it  becomes  necessary  to  transpose  the  com- 
bination, so  that  it  is  ground  on  a  —  6  D.  base.  It  is  preferable, 
however,  to  grind  these  combinations  on  a  9  D.  base.  For  ex- 
ample, +  3  =  -f  I,  if  ground  on  a  -f  6  D.  base,  would  have  but 

—  3  inside  curve.    If  ground  on  a  +  9  D.  base  curve  it  would  be 

—  6  D.  on  the   inside.     It  could   be  transposed,   however,   and 


138 


The  Making  of  a  Mechanical  Optician 


ground  on  a  —  6  D.  base  curve  and  it  would  be  —  6  D.  on  the 
inside  and  +  lo  D.  on  the  outside.  It  should  be  remembered 
that  the  base  curve  is  always  the  weakest  meridian  on  the  cylinder 
side ;  that  is,  a  +  6  D.  base  curve  is  -|-  6  in  one  meridian  and 
stronger  in  the  other.  The  difference  will  be  the  power  of  the 
cylinder.  A  —  6  D.  base  is  —  6  D.  in  one  meridian  and  stronger 
in  the  other.  The  spherical  power  is  obtained  by  grinding  the 
opposite  side. 

Another  point  to  keep  in  mind  is  that  concave  toric  cylinders 
cost  more  than  convex,  and,  whenever  possible,  all  combinations 
should  be  transposed  so  that  a  plus  cylinder  can  be  used.     For 


Fig.  163 


example,  in  the  combination  —  i  =  —  .50,  if  it  is  ground  as 
written  a  —  .50  toric  cylinder  would  be  selected  and  the  cylinder 
surface  would,  of  course,  be  on  the  inside.  On  the  outside  would 
then  be  ground  -\-  5,  thus  making  the  —  i  sphere.  If  this  were 
transposed  to  —  1.50  =  -|-  50,  a  +  .50  toric  cylinder  would  be 
selected  and  —  7.50  ground  on  the  inside  to  produce  the  —  1.50 
sphere.  The  reason  that  concave  toric  cylinders  cost  more  is  that 
the  large  factories  have  not  as  yet  perfected  machines  for  grind- 
ing these  in  quantity  the  same  as  the  convex,  and,  consequently, 
they  are  ground  singly  at  a  greater  expense. 

When  selecting  colored  lenses  it  is  necessary  to  have  in 
mind  that  as  the  glass  is  ground  thinner  the  shade  will  be  much 
lighter,  and  it  is  a  very  difficult  matter  to  judge  just  how  they  are 
coming  out.     For  this  reason  colored  lenses  with  power  are  al- 


The  Making  of  a  Mechanical  Optician  139 

ways  expensive  as  a  great  many  times  it  is  necessary  to  grind 
two  or  three  pairs  before  the  exact  shade  is  produced.  The  de- 
mand for  colored  lenses,  however,  is  so  unimportant  that  they 
call  for  little  consideration  as  compared  with  the  colorless  variety. 

For  wafers,  spherical  lenses  are  used,  but  always  selected 
so  that  one  surface  is  correct.  For  this  Pcx.  lens  always  work 
in  nicely  as  the  old  curves  can  always  be  found.  For  example, 
for  the  combination  —  i  =  -(-  3.50,  a  +  2.25  Pcx.  would  be 
selected,  and  this  would  be  on  the  outside  +  3.50  and  on  the  in- 
side —  1-25.  We  would  then  block  it  with  the  convex  surface 
down  and  regrind  the  inner  to  —  i,  at  the  same  time  reducing  the 
thickness  to  whatever  is  desired. 

Spherical  prisms  can  be  ground  on  rough  prisms  or  a  stronger 
piano  prism  can  be  used  to  get  the  thickness  required. 


CHAPTER  XIII 


SURFACE  GRINDING — Continued 

The  machine  now  behig  in  operation,  and  the  emery  arranged 
conveniently,  the  first  operation  will  be  to  mark  the  lens.  If  a 
brown  pitch  is  used  in  blocking,  black  ink  will  show  well  enough, 
but  if  black  pitch  is  used,  white  ink  is  much  better.  If  a  simple 
compound  is  to  be  ground,  no  marks  are  required,  but  with  all 
prism  combinations  the  axis  must  be  marked.  This  method  is 
the  same  as  for  cutting,  except  that  it  must  be  taken  into  con- 
sideration that  when  the  lens  is  on  the  block,  you,  perhaps,  are 
looking  at  it  from  the  wrong  side.  This,  of  course,  depends  on 
the  combination.  For  example,  if  the  combination  to  be  ground 
is  —  50  axis  45  =  1°  in,  the  lens  can  be  marked  with  the 
cylinder  in  (or  up,  as  it  is  laid  on  the  protractor)  just  as  it  is 
to  be  fitted  to  the  spectacle. 

It  is,  of  course,  necessary  to  mark  all  lenses  on  the  cylinder 
side,  otherwise  the  marks  will  be  ground  off.  When  this  is  stuck 
on  the  block  the  cylinder  will  be  down,  and  you  are  really 
working  on  it  as  though  the  axis  was  135°.  On  the  other  hand, 
if  the  combination  is  +  5°  axis  45  =  1°  in,  it  would  be  necessary 
to  mark  it  as  if  it  were  to  be  135°.  The  reason  for  this  is  that 
you  are  marking  it  on  the  cylinder  side,  and  after  this  is  com- 
pleted, it  is  to  be  fitted  to  the  spectacle  with  this  side  out.  The 
reason  for  marking  is  to  have  a  line  to  grind  the  prism  on,  in 
other  words,  to  tell  the  direction  of  the  base.  If  this  is  to  be  in, 
the  axis  must  be  set  at  the  proper  angle  so  that  the  prism  line 
must  be  horizontal.  It  does  not  matter,  however,  how  this  is 
placed  on  the  block  as  long  as  the  relative  position  of  the  axis  to 
the  base  is  correct. 

If  a  double  prism  is  to  be  ground,  that  is,  a  lens  with  the 
prism  out  and  up,  etc.,  it  will  be  necessary  to  have  a  line  for  both 
prisms.  In  marking,  the  axis  is  first  dotted  and  laid  on  the  pro- 
tractor at  the  proper  angle,  the  prism  lines  are  then  drawn  and 
the  bases  marked  with  the  letter  "B".  As  the  prism  lines  are 
the  onlv  ones  that  are  considered,  the  axis  dots  can  then  be  rubbed 


The  Making  of  a  Mechanical  Optician  141 

out  if  preferred  to  save  confusion.  There  is  a  chart  published 
for  calculating  the  effect  of  double  prisms  that  is  very  con- 
venient, but  it  is  not  absolutely  necessary  to  use  this  in  surface 
grinding.  A  double  prism  is  really  a  single  prism  ground  at  a 
different  angle.  For  example,  a  2°  up  :=  2°  out  in  the  right  eye 
would  be  practically  a  3°  axis  135°. 

For  blocking,  an  ordinary  cheap  gas  stove  is  sufficient,  but 
a  piece  of  sheet  iron  should  be  laid  over  the  top  to  prevent  any 
pitch  running  down  into  the  stove  and  clogging  the  holes.  The 
blocks  should  be  heated  on  the  stove,  and,  when  good  and  hot, 
should  be  taken  off  and  placed  on  the  bench.  A  little  pitch  should 
then  be  put  on  and  allowed  to  melt.  The  glass  to  be  blocked 
should  be  warmed  slightly  and  laid  on  the  block  a  second  and 
then  removed.  It  will  be  noticed  that  some  of  the  pitch  sticks 
to  the  surface.  A  little  more  of  the  pitch  should  then  be  put  on 
the  block  and  the  lens  laid  on  a  second  time,  and  then  removed. 
In  this  way  you  gradually  build  up  a  backing  for  the  lens.  This 
operation  should  be  repeated  several  times  until  there  is  pitch 
enough  between  the  block  and  the  lens  so  that  it  will  hold 
securely,  and  also  that  there  is  no  danger  of  the  glass  touching 
the  iron.  This  not  only  prevents  scratching,  but  if  there  is  not 
pitch  enough  to  form  a  good  bed  for  the  glass,  it  will  crack 
when  pressure  is  applied  in  grinding. 

Flat  lenses  do  not  require  as  much  pitch  as  those  having  a 
concave  surface  or  a  toric.  Ordinary  concave  lenses  can  be 
blocked  on  flat  blocks,  but  care  must  be  used  to  fill  up  the  space 
with  pitch  for  the  reason  just  stated.  For  convex  toric  cylinders, 
a  block  having  a  concave  surface  should  be  used,  and  although 
the  curve  should  be  about  the  same,  it  is  not  absolutely  necessary, 
as  the  surface  can  be  built  up  with  pitch.  For  concave  toric 
cylinders,  convex  blocks  should,  of  course,  be  used.  After  the 
lenses  are  blocked,  they  should  be  allowed  to  cool  gradually. 
After  they  are  cool,  the  pitch  on  the  back  of  the  lens  that 
overhangs  the  block  should  be  scraped  off  with  a  knife  so  that 
the  four  sides  can  be  measured  with  the  calipers.  Lenses  can 
also  be  blocked  over  an  ordinary  Bunsen  burner,  and  if  it  is 
done  in  this  way,  the  pitch  should  be  moulded  into  sticks  and 
melted  on  the  block  the  same  as  sealing  wax  is  used. 

We  will  suppose  that  the  combination  to  be  ground  is  +  i 


142  The  Making  of  a  Mechanical  Optician 

=  +  50  cyl.  and  l  1/2  strap  on  the  edge  when  finished.  We 
have  selected  a  +  5°  cyhnder,  2  1/2  mm.  thickness,  and  have 
blocked  it  as  described.  We  then  select  the  tool  to  grind  + 
I  sph.  This,  of  course,  will  be  a  concave  tool  to  gfrind  a  convex 
surface.  It  should  be  tried  with  the  gage  to  see  if  it  is  correct. 
The  rough  emery  is  already  in  the  pan,  with  plenty  of  water. 
The  block  or  lens  is  then  taken  in  the  left  hand  and  held  on  the 
tool,  spooning  the  emery  on  with  the  right  hand.  After  the  sharp 
edges  are  ground  off,  the  block  can  then  be  placed  under  the 
spindle  in  the  handle.  It  will  then  be  necessary  to  adjust  this  so 
the  lens  is  in  the  center  of  the  tool.  As  to  position,  the  grinder 
can  stand  wherever  it  is  most  natural.  Some  of  the  older  ma- 
chines are  arranged  so  that  the  handle  points  directly  to  the 
operator,  and  some  use  it  in  this  position ;  others  stand  a  little  to 
one  side.  In  either  case  this  is  somewhat  awkward  and  the  best 
wav  is  to  have  the  handle  run  from  right  to  left,  so  that  it  is  in 
a  horizontal  position  to  the  grinder. 

The  newest  machines  are  made  so  that  they  can  be  adjusted 
to  any  position.  When  the  handle  has  been  adjusted  correctly, 
the  machine  can  be  started.  The  lens  will  then  revolve  or  spin 
on  the  spindle,  and  the  grinder  then  moves  the  handle  forward 
and  back  so  that  the  lens  will  travel  from  the  center  to  the  edge 
of  the  tool.  This  motion  is  to  break  up  the  rings  which  would 
form  on  the  surface  of  the  glass  if  it  were  held  in  one  position. 
One  must  be  careful,  however,  not  to  run  over  the  center  of  the 
tool,  or  the  block  may  fly  off.  As  the  lens  is  moved  back  and 
forth,  the  emery  should  be  fed  continually  with  the  spoon.  After 
the  lens  has  ground  a  minute  or  two,  it  should  be  removed,  and 
if  it  is  ground  all  over  the  surface,  it  is  ready  to  measure.  Now 
take  the  calipers  and  measure  all  four  edges.  If  it  is  the  same 
all  around,  the  lens  is  centered  and  not  prismatic.  If  there  is  a 
difference,  take  the  block  in  the  hand  the  same  as  when  starting 
and  grind  oft'  a  little  of  the  thick  edge,  tlien  measure  again.  If 
found  correct,  it  can  then  be  placed  on  the  spindle  again  and 
ground  as  before. 

The  system  of  measuring  should  be  remembered,  that  is, 
2/5  mm.  allowance  for  every  diopter.  As  we  started  with  a  lens 
2y,  mm.  thick  and  wish  to  obtain  a  lens  15-2  mm.  it  will  be  neces- 
sary to  grind  off  i  mm.  or  5/5  on  the  calipers.     In  the  roughing 


The  Making  of  a  Mechanical  Optician  143 

about  2/5  mm.  will  be  taken  off,  being  careful,  of  course,  to  keep 
it  centered  as  described.  Do  not  be  afraid  to  measure  it  too 
much,  for  it  is  better  to  take  oft'  a  little  at  a  time  than  to  spoil  the 
lens.  After  it  has  been  roughed  down,  wipe  off  the  tool  and  rinse 
the  lens  in  water.  (For  this  purpose,  keep  a  pail  at  the  side  of 
the  machine.)  Now  take  the  No.  100  emery,  which  is  in  the  cup, 
and  grind  as  before,  smoothing  the  surface  and  taking  off'  about 
1/5  mm.  Then  wipe  off  the  tool  again,  rinse  the  lens  and  take 
the  No.  4-F  emery.  This  you  can  apply  with  the  fingers,  or  a 
brush  if  preferred.  After  this  grade,  clean  the  lens  and  tool 
again  thoroughly  and  you  are  ready  for  the  fine  finishing.  For 
this  operation  it  is  necessary  to  use  but  very  little  of  the  finest 
emery,  applying  it  with  one  finger.  The  idea  now  is  to  get  just 
as  fine  a  surface  as  possible  to  obtain  next  to  a  polish. 

Although  it  is  unnecessary  to  waste  the  emery,  all  scratches 
and  pits  must  be  removed,  as  time  is  not  only  wasted  in  trying 
to  polish  them  out,  but  the  lens  produced  is  not  so  good.  It 
should  also  be  remembered  that  this  grade  of  emery  is  expensive. 
All  through  these  different  operations  keep  in  mind  that  the  lens 
must  be  calipered  frequently  to  keep  it  from  being  prismatic, 
and  also,  that  as  you  are  continually  grinding  off  glass,  you  are 
Hearing  the  thickness  required  for  the  finished  lens.  Also  be 
particular  to  clean  the  tool  and  the  lens  between  each  grade  of 
emery  used,  as  one  grain  of  rough  emery  on  the  tool  when  fine 
finishing  will  scratch  the  surface. 

If  the  combination  was  —  i  =  —  50,  the  operation  would 
have  been  the  same,  using,  of  course,  the  opposite  tool,  but  if 
the  order  called  for  a  certain  thickness  in  the  center,  the  lens 
would  be  2/5  mm.  thicker  on  the  edge.  Although  this  has  to 
be  taken  into  consideration  in  convex  combinations,  allowing  the 
lens  to  be  2/5  mm.  thinner  on  the  edge  than  on  the  center,  it 
does  not  make  quite  so  much  difference,  for  the  reason  that  the 
concave  lens  is  apt  to  be  ground  through  the  center.  This  will 
be  noted  in  grinding  the  stronger  combinations,  and  one  must  be 
accurate  in  measuring  when  selecting  rough  cylinders. 

For  each  prism  diopter  4/5  mm.  must  be  allowed,  so  if  the 
combination  to  be  ground  was  -f-  i  =  +  50  axis  90°  ^  1°  in, 
we  would  allow  2/5  mm.  for  the  sph.  and  4/5  mm.  for  the 
prism,   making   i  1/5   mm.   besides   the   allowance   for  grinding. 


144  J^^'^  Making  of  a  Mechanical  Optician 

We  have  already  described  the  method  of  marking  for  a  prism, 
and  the  blocking  is  the  same  as  for  a  comf)ound.  In  starting 
to  grind,  the  lens  is  held  in  the  hand,  not  on  the  spindle, 
as  before,  but  we  grind  off  the  edge  where  the  apex  is  to  be, 
leaving  the  edge  for  the  base  as  thick  as  possible.  It  will  now  be 
seen  why  it  was  necessary  to  mark  a  mechanical  axis  or  prism 
line.  It  should  be  measured  on  this  line,  and  the  base  should  be 
4/5  mm.  thicker  than  the  apex.  The  two  opposite  sides  are  of 
no  account,  except  that  they  should  be  exactly  the  same  thickness. 
If  one  was  thicker  than  the  other,  there  would  then  be  a  prism 
power  up  or  down  as  well.  By  this  it  will  be  seen  how  to  grind 
a  double  prism.  For  example,  if  the  combination  was  to  be 
+  I  =  +  50,  axis  90°  =  1°  in  and  1°  up,  we  would  have 
4/5  mm.  difference  on  the  edge  between  the  apex  and  base  on 
the  180°  line,  and  also  4/5  mm.  difference  on  the  90°  line.  When 
the  lens  has  been  roughed  down  in  the  hand  so  that  the  prism 
power  is  approximately  correct,  it  can  be  placed  on  the  spindle 
and  roughed  down  to  the  proper  thickness.  It  should  be  re- 
membered that  all  the  prism  power  must  be  roughed  on  with 
the  block  in  the  hand,  and  that  the  lens  cannot  be  ground  pris- 
matic on  the  spindle.  This  does  not  mean  that  the  lens  will 
not  grind  prismatic  because  it  will  grind  off  center  more  or  less, 
but  it  means  that  you  cannot  control  the  direction  of  the  prism 
power  on  the  spindle.  As  different  grades  of  emery  are  used, 
the  edge  must  be  measured  constantly,  and  if  there  is  any  variation 
found,  take  the  lens  in  the  hand  again  and  true  it  up  with  what- 
ever grade  of  emery  you  may  be  using. 

In  grinding  a  cylinder  prism,  the  plane  too!  is  used,  and 
the  prism  power  only  has  to  be  considered.  For  example,  a  -j-  50 
axis  45  ^  I  in  would  be  marked  and  blocked  as  usual,  and  the 
apex  ground  to  the  proper  thickness,  say  2  mm.  The  base  should 
then  be  2  4/5  mm.  thickness.  The  plane  tool  should  be  kept  as 
accurate  as  possible  for  the  reason  that  the  slightest  spherical 
power  can  readily  be  detected  on  the  axis  of  a  piano  cylinder. 
This  is  also  a  difiScult  lens  to  polish,  as  will  be  explained.  It 
should  be  remembered  that  a  piano  lens  is  the  most  difficult  to 
grind. 

In  grinding  the  wafers,  it  is  only  necessary  to  grind  them 
small  enough  to  be  thin.     The  spherical  lens  is  blocked,  putting 


The  Making  of  a  Mechanical  Optician  i45 

the  surface  that  is  correct  down  on  the  block,  of  course,  and 
crind  it  down  to  about  30  mm.  diameter.  For  horseshoe-shaped 
wafers  they  can  be  ground  smaller,  but  if  less  than  25  mm.  they 
will  be  too  thin  to  handle. 

Tories  are  ground  the  same  as  a  regular  compound,  obtam- 
in-  the  rough  toric  cylinders  from  the  jobbers.  If  the  com- 
bination to  be  ground  is  -f  i  =  50,  a  +  50  toric  rough  cylinder 
is  selected,  and  this  will  have  the  cylinder  on  the  outside,  ihis 
is  blocked  with  the  surface  down,  and  —  5  ground  on  the  mside. 
It  should  be  remembered  that  these  should  be  blocked  on  concave 
blocks  so  that  the  surface  will  fit. 

If  any  amount  of  roughing  is  to  be  done,  do  it  on  the  e.xtra 
tool  kept  for  this  purpose.  This  should  be  about  6  D.  curve,  and 
it  is  not  necessary  to  keep  it  accurate.  The  idea  is  simply  to  have 
a  tool  with  strong  power  to  save  the  regular  tools.  Rough  emery 
grinds  the  tool  very  quickly,  and,  consequently,  throws  it  out 
of  true.  Quite  a  little  time  must  then  be  spent  to  keep  them 
in  shape. 


CHAPTER  XIV 


SURFACE  GRINDING— Continued 
Toric  and  Special  Lenses 

Toric  lenses  are  ground  in  the  same  way  as  compounds;  that 
is,  the  spherical  side.  The  rough  toric  cylinders  are  obtained 
from  the  jobbers  in  the  moulded  form,  and  this  reduces  the 
labor  considerably.  When  it  was  necessary  to  grind  them  from 
the  flat  form  a  great  deal  of  roughing  had  to  be  done.  The 
blocking  has  already  been  described,  and,  if  this  is  properly  done, 
there  is  very  little  danger  of  breaking.  In  grinding  torics  it  is 
very  difficult  to  get  the  spherical  power  accurate  for  the  reason 
that  in  grinding  strong  curves  a  little  variation  can  hardly  be 
detected,  but  when  the  curve  is  ground  on  the  opposite  side 
the  total  power  of  the  lens  is  so  weak  as  compared  to  the  surfaces 
ground,  that  it  is  a  very  easy  matter  to  grind  the  power  .12  D. 
weaker  or  stronger.  For  this  reason  torics  should  be  ordered 
of  reliable  houses  that  give  this  matter  proper  attention.  One 
should  also  be  particular  to  notice  whether  B.  &  L.  or  A.  O.  Co. 
rough  toric  cylinders  are  used.  If  an  A.  O.  Co.  piano-cylinder 
is  to  be  ground  on  a  B.  &  L.  tool  it  should  be  6.18  to  be  exact. 
(6.12  will  be  near  enough.)  If  a  B.  &  L.  piano-cylinder  is  to 
be  ground  on  an  A.  O.  Co.  tool,  it  should  be  5.82  (5.87  will 
answer). 

If  a  -f-  I  =  +  50  is  to  be  ground,  a  -f-  50  toric  cylinder 
with  +  6  D.  base  curve  is  selected,  and  —  5  D.  spherical  ground 
on  the  inside.  For  +  2  ^  -f-  50,  a  —  4  D.  spherical  would  be 
ground  on  the  inside,  and  so  on.  As  the  spherical  power  in- 
creases, the  inside  curve  decreases,  so  that  if  the  full  toric  elfect 
is  desired  it  will  be  necessary  to  transpose  the  combination  and 
grind  it  on  a  concave  cylinder. 

If  a  —  I  =  —  50  is  to  be  ground,  a  — -50  cylinder  with 
—  6  D.  curve  is  selected,  and  +  5  sph.  ground  on  the  outside. 
Remember  that  the  base  is  always  6  D.,  and,  to  produce  the  re- 
quired spherical,  simply  deduct  the  power  desired,  and  this  will  be 
the  curve  to  grind.  Also  do  not  forget  that  when  grinding  a  -j- 
and  -f-  combination  on  a  —  cylinder  that  the  combination  must 


The  Making  of  a  Mechanical  Optician  147 

be  transposed.  This  is  the  cause  of  many  mistakes.  For  example : 
_|_  I  =  -|-  50  if  ground  on  a  +  cyHnder  will  have  a  —  5  inside 
curve,  or  i  D.  weaker  than  the  base.  When  transposed  it  will 
be  +  1.50  =  —  50,  and  the  outside  curve  will  be  +  7.50,  or 
1.50  D.  stronger  than  the  base.  When  9  D.  base  curve  is  re- 
quired plus  cylinders  can  most  always  be  used,  and  it  is  rarely 


Fig.  164 

necessary  to  use  minus.     The  curves  are  not  only  extreme,  but 
the  rough  concave  cylinders  are  expensive. 

Toric  cylinders  are  usually  ground  on  automatic  machines, 
although  a  hand  attachment  for  the  regular  surface  machines 
can  be  obtained  (Fig.  164).  This  work  at  present  is  not  attempted 
by  opticians,  except  in  large  shops  or  in  localities  where  it  re- 
quires some  time  to  obtain  the  rough  stock.  As  the  sale  of 
fused  bifocals  increase,  however,  more  opticians  will  be  obliged 
to  grind  cylinder  or  toric  surfaces  if  they  give  prompt  service  to 
their  customers.  The  hand  attachment  requires  special  blocks, 
having  an  iron  rod  running  through  the  center  (Fig.  165),  to 
keep  the  axis  of  the  lens  in  line  with  the  tool.  If  the  cylinder 
is  fairly  strong  it  will  save  time  and  also  the  wear  on  the  tools 
to  rough  a  spherical  power  on  the  glass  first.  It  is  then  placed 
on  the  cylinder  tool  and  the  cylinder  power  put  on  with  3-F 
carborundum.  This  material  cuts  faster  than  emery  and  leaves 
a  smooth  surface.  The  machine  can  be  run  at  almost  any  speed, 
but  for  the  beginners  it  is  better  to  use  about  600  revolutions 


148  The  Making  of  a  Mccliaiiical  Optician 

per  minute.  It  is  operated  by  the  hand  lever,  the  same  as  when 
grinding  a  spherical,  but  it  is  necessary  to  stop  the  machine  to 
feed  it.  Care  must  also  be  used  to  keep  the  lens  on  the  tool,  as 
a  slip  is  apt  to  not  only  spoil  the  lens,  but  the  arms  of  the 
machine  can  also  be  broken  very  easily.  After  the  carborundum. 
No.  4-F  emery  can  be  used  and  then  the  washed  emery.  The 
operations  are  the  same  as  when  grinding  sphericals,  except  that 
it  reqviires  a  great  deal  more  time.  For  those  that  can  afford 
it,  the  automatic  machines  are  to  be  preferred,  but  they  usually 
require  much  more  time.  There  is  a  new  machine  just  placed 
on  the  market,  however,  that  will  grind  a  pair  of  lenses  quicker 
than  a  pair  of  sphericals  can  be  ground  by  hand  (Fig.  166).  This 
will  be  of  great  benefit  to  the  trade  generally,  as  time  is  the  most 
important  part  of  the  business  to-day,  except,  of  course,  accuracy. 

Another  machine  that  is  used  quite  extensively  is  the  "Her- 
cules" (Fig.  167).  This  machine  does  not  require  a  separate 
spindle,  but  fits  the  spindle  of  any  hand  surface  grinder.  It  does 
not  revolve,  but  the  spindle  simply  drives  the  lens-moving 
mechanism. 

Prescription  houses  are  frequently  asked  if  certain  com- 
binations, especially  prisms,  can  be  made  in  torics.  All  combina- 
tions of  lenses  can  be  ground  in  toric  form,  but  sometimes  no 


Fig.  165 

better  results  are  obtained.  For  example,  —  12  =  —  i  would 
be  an  extreme  curve  if  ground  in  toric  form,  as  the  inside  curve 
would  be  —  19  D.  It  would  be  much  better  to  make  it  in  double 
concave  form  with  —  6  spherical  on  one  side  and  —  6  =  —  7 
on  the  other.  If  this  form  was  not  desired,  it  would  be  better 
to  make  it  in  the  regular  compound  form. 


The  Making  of  a  Mechanical  Optician  149 

It  is  also  a  common  idea  that  strong  concave  combinations 
are  thinner  when  ground  in  toric  form.  This  is  entirely  wrong, 
and  the  only  way  to  grind  these  is  to  make  them  lenticular.  A 
lenticular  lens  is  one  having  the  power  in  the  center  only,  usually 
in  a  circle,  having  a  diameter  of  22  mm.  This  is  the  stock  form, 
but  they  can  be  ground  with  the  circle  as  large  as  the  width  of 
the  lens.  The  larger  the  circle,  the  thicker  the  lens, 
however.  Outside  the  circle  is  usually  piano,  but  when  a  large 
circle  is  desired,  the  outside  can  be  ground  convex.  This 
reduces  the  thickness  on  the  edge,  so  that  it  may  be  as  thin  as 
desired.  This  style  of  lens  can  also  be  made  with  an  oval  center, 
but  these  are  quite  difficult,  and  it  is  best  to  order  them  from  the 
prescription  houses.  Lenticular  lenses  are  very  desirable  and 
should  be  used  more,  and  the  reason  that  they  are  not  is  that 
opticians  are  not  generally  familiar  with  the  different  forms,  or 
else  they  believe  that  the  field  is  limited. 

In  grinding  lenses  this  style  the  first  operation  is  to  grind 
the  power  in  the  center,  the  same  as  any  regular  lens.  This 
may  be  ground  away  out  to  the  edge  if  desired.  It  is  perhaps, 
just  as  well  to  do  this  w-hen  the  power  is  not  strong,  but  in  the 
higher  power  lenses  it  requires  too  thick  stock  and  it  also  makes 
unnecessary  work.  After  the  focus  is  ground  and  polished  the 
center  should  be  filled  with  sealing  wax  and  then  the  piano  tool 
and  grind  off  until  the  circle  is  the  correct  size.  This  should  not 
be  over  25  mm.,  unless  the  focus  is  not  over  10  D.  If  higher 
than  this,  it  makes  a  better  lens  to  grind  it  convex.  The  power 
of  the  outside  curve  will  depend  on  the  size  of  the  circle  desired, 
also  the  focus  of  the  lens.  The  curve  required  will  vary  from 
6  D.  upward,  and,  until  you  are  experienced,  it  is  a  good  plan 
to  select  a  low  power  and  try  it.  If  the  curve  is  not  steep 
enough,  try  a  stronger  one.  The  outside  surface  should  be 
polished  before  the  wax  is  removed.  In  referring  to  the  outside 
curve  of  this  style  lens  we  mean  the  curve  outside  the  circle 
and  not  on  the  opposite  side  of  the  lens. 

Fused  bifocals  are  very  interesting  to  .grind,  and  as  the 
blanks  can  now  be  obtained,  the  most  difficult  part  has  already 
been  done.  In  ordering  the  blanks,  it  is  necessary  to  give  the 
full  prescription,  so  that  the  proper  blank  can  be  selected.  It 
must  be  remembered  that  the  curve  ground  on  the  disk  side 
will  change  the  addition,  so  this  must  be  taken  into  account. 


ISO 


The  Making  of  a  Mechanical  Optician 


It  is  also  impossible  to  grind  a  cylinder  on  the  disk  side  for  this 
reason  so  in  compounds  an  allowance  for  the  spherical  must  be 
made.  In  making  the  blanks,  a  depression  is  ground  in  the  base 
lens  of  a  certain  power,  the  curve  having  been  calculated  for 
the  index  of  the  flint  to  be  used  for  the  disk.  For  example:  If 
a  lo  D.  will  produce  2.50  D.  addition,  each  diopter  will  add 
-f-  .25.  If  the  blank  was  intended  for  a  piano  surface  and  a  +  i 
was  ground  on  it,  it  would  increase  the  reading  addition  .25  D. 
By  this  it  will  be  seen  that  if  the  prescription  called  for  distance 


Fig.  166 


-(-  I  =  —  50  axis  90,  reading  +  3-50,  and  the  blank  used  was 
intended  for  a  piano  surface,  the  lens  when  finished  would  have 
for  reading  +  3.75.  The  blanks  are  blocked  the  same  as  any 
lens,  but  care  must  be  used  in  heating. 

If  the  lens  was  not  properly  annealed  it  is  very  liable  to 
break.  The  disk  side  is  always  ground  first,  as  this  must  be 
brought  down  to  the  proper  size.  This  is  the  most  particular 
part  of  the  work,  as  it  can  be  easily  ground  too  small.  After 
the  flint  is  ground  ofiF  so  that  the  surface  is  even  it  should  be  fined 


The  Making  of  a  Mechanical  Optician  151 

down  very  slowly,  as  this  glass  is  very  soft  and  grinds  away 
quickly.  In  grinding  a  pair,  always  grind  both  disk  surfaces 
first,  so  that  the  disks  can  be  made  the  same  size.  Frequently, 
one  lens  will  be  ground  so  that  the  disk  is  the  correct  size,  and 
then  the  other  will  have  a  scratch  or  imperfection  in  it,  so  that 
it  must  be  ground  smaller.  It  will  then  be  necessary  to  reduce 
the  other  to  match.  In  this  way,  grinding  first  one  and  then  the 
other,  it  is  possible  to  get  them  to  match.  After  the  disk  side  is 
ground,  the  other  side  can  be  brought  down  so  as  to  make  the 
finished  lenses  the  proper  thickness.  If  a  cylinder  is  to  be  ground 
on  the  other  side,  it  will  be  necessary  to  mark  the  axis,  as  the 
disk  must  be  in  the  proper  position.  If  the  lens  is  twisted  to 
correct  the  axis  after  the  lens  is  finished  the  disk  will  be  out  of 
center.  If  the  axis  is  found  to  be  off,  it  must  be  blocked  again 
and  reground. 

When  the  lens  is  laid  out  for  axis,  always  try  the  tool  with 
lens  measure  and  see  if  the  axis  is  in  the  proper  position.  There 
is  nothing  difficult  in  grinding  these  lenses,  but  grind  slowly, 
taking  off  a  little  at  a  time.  In  polishing,  remember  that  the  fiint 
is  soft  and  is  easily  made  wavy. 

When  the  lens  is  ground  and  the  finish  is  as  near  perfect 
as  possible,  the  lens  is  ready  to  polish.  The  tool  should  be 
cleaned  and  the  lens  rinsed  in  water.  Then  take  a  piece  of  felt, 
either  round  or  square,  as  you  prefer,  and  stick  it  on  the  tool. 
The  material  used  is  called  "Tacky,"  and  this  is  made  from 
powdered  rosin,  or  pitch,  the  same  as  used  for  blocking,  and 
cut  with  alcohol,  so  that  it  is  in  the  form  of  a  paste.  This  is  first 
applied  to  the  surface  of  the  tool  with  a  brush,  while  it  is  running. 
The  machine  is  then  stopped  and  the  felt  pressed  down  firmly. 
Then  start  the  machine  and  with  a  knife  trim  off  the  corners 
near  the  edge  of  the  tool.  This  is  where  the  art  of  polishing 
a  lens,  weak  or  strong,  comes  in.  A  convex  lens  may  be  polished 
strong  by  cutting  the  cloth  large,  and  weak,  by  cutting  the  cloth 
small.  A  concave  will  be  just  the  opposite,  the  lens  will  be 
strong  when  polished  on  a  small  cloth  and  weak  on  a  large  cloth. 

The  rouge  should  be  placed  in  a  cup  and  mi.xed  with  water, 
so  that  it  will  be  in  the  form  of  a  paste;  then  place  aside  of  this 
another  cup  containing  plain  water.  Now  apply  the  rouge  with 
a  brush,  so  that  the  felt  will  be  well  saturated;  then  place  the 


152 


The  Making  of  a  Mcclianical  Optician 


lens  on  the  spindle  and  start  the  machine.  As  the  lens  revolves, 
move  the  lever  forward  and  back,  the  same  as  when  grinding  to 
break  up  the  rings  that  would  form  if  it  were  held  in  one  position. 
Apply  the  rouge  occasionally,  but  do  not  let  it  get  too  dry,  so 
that  it  will  cake  on  the  cloth.  If  it  has  this  appearance,  apply  a 
little  water.  A  lens  will  polish  faster  with  a  fairly  dry  cloth,  but 
it  cannot  be  too  dry,  of  course.  After  polishing  for  two  or 
three  minutes,  take  the  lens  ofif  the  spindle  and  examine  the  sur- 
face. For  this  purpose  a  gas  flame  will  give  better  results,  as  it 
has  more  or  less  flare.     Daylight  will  answer,  but  electric  light 


Fig.  167 


is  not  very  good.  The  lens  should  be  held  in  the  hand,  a  little 
below  the  level  of  the  eyes,  in  such  a  position  that  a  good  reflection 
of  the  flame  will  be  found  on  the  surface  of  the  glass.  By  tilting 
it  gradually  so  that  the  reflection  moves  across  the  surface,  it  will 
show  up  any  imperfections,  such  as  pits  or  scratches.  When  the 
glass  has  but  a  slight  polish,  the  emery  marks  will  be  seen  and 
these  must  be  polished  out. 

After  the  first  inspection,  and  the  lens  has  been  found  free 
from  large  pits  and  scratches,  replace  it  on  the  spindle  and  polish 
a  few  minutes  longer  and  then  inspect  again.  As  soon  as  the 
emery  marks  have  all  disappeared  the  lens  is  polished.  If  for 
any  reason  a  scratch  appears,  or  a  pit  of  any  size  is  found,  it  is 


The  Making  of  a  Mechanical  Optician  153 

best  to  finish  it  again  with  the  washed  emery,  as  this  will  not 
only  save  time,  but  a  better  lens  will  be  produced.  When  a  lens 
is  polished  too  long,  the  power  is  apt  to  be  olT,  so  that  the  quicker 
it  is  polished  the  better.  Remember,  however,  that  it  will  take 
just  about  so  much  time  to  polish  a  lens,  and  that  just  putting 
a  glaze  on  the  surface  is  not  a  polish.  Beginners  are  very  liable 
to  make  this  mistake,  and  it  requires  quite  a  little  practice  to  judge 
the  surface  of  a  lens.  The  cloth  can  be  used  several  times,  and, 
in  fact,  until  it  wears  down  too  thin.  When  polishing  a  piano 
surface,  such  as  a  cylinder  prism,  never  use  a  new  cloth,  but  al- 
ways use  one  that  has  been  used  before.  The  nap  on  a  new  one 
will  sometimes  produce  aberration. 

To  remove  a  lens  from  the  block,  place  it  under  a  running 
faucet  for  several  minutes.  If  the  pitch  is  then  started  a  little 
with  a  knife,  the  glass  will  come  off  easily.  The  lens  should 
then  be  placed  in  a  basin  of  turpentine  to  eat  oflf  the  pitch. 


CHAPTER  XV 


SOLDERING  AND  REPAIRING— THE  EQUIPMENT 

Soldering  is  a  part  of  mechanical  optics  not  attempted  by 
many  opticians.  While  it  is  not  very  profitable,  perhaps,  it  must  be 
done  occasionally  to  satisfy  a  customer.  It  also  frequently  hap- 
pens that  it  must  be  done  in  a  hurry,  as  there  is  no  time  to  send 
it  away.  There  are  many  jobs  that  opticians  are  called  upon  to 
do  in  the  way  of  small  repairs  and  one  thing  that  is  necessary 
is  to  have  proper  equipment  and  the  work  then  will  not  be  difficult. 

Gas  is  very  essential  to  do  good  soldering,  although  it  can 
be  done  with  an  alcohol  lamp.  Alcohol  is  very  unsatisfactory, 
for  the  reason  that  it  is  impossible  to  obtain  a  large  flame  and, 
therefore,  there  is  not  heat  enough. 

There  are  several  ways  of  arranging  the  gas,  and  possibly 
the  simplest  is  to  use  an  ordinary  swinging  gas  bracket  and  re- 
move the  lava  tip.  The  size  of  the  flame  can  then  be  regulated 
and  an  ordinary  blowpipe  used  (Fig.  i68).    There  are  two  styles. 


Fig.  168 — Blowpipe 

one  having  a  bulb,  forming  a  sort  of  reservoir  for  air.  Either 
will  do,  however.  There  are  also  a  number  of  different  styles 
of  blowpipes  that  are  used  principally  by  dentists.  Some  styles 
are  quite  elaborate,  having  valves  to  regulate  the  air  arid  also  the 
gas.  These  are  not  necessary,  however,  as  one  can  be  made 
very  easily  that  would  be  simpler  and  better.  It  consists  of  a 
brass  pipe  with  a  rubber  tube,  which  is  attached  to  the  gas  at  any 
convenient  place,  and  another  tube  is  inserted  at  an  angle  of  45° 
On  this  is  another  rubber  tube,  which  is  held  in  the  mouth.  An 
ordinary  pipe  mouthpiece  can  be  used  if  desired  to  hold  in  the 
mouth.  The  drawing  (Fig.  169)  gives  a  good  idea  of  the  con- 
struction. A  blowpipe  of  this  kind  can  be  held  in  the  hand 
in  any  position  and  is,  therefore,  much  more  convenient. 


The  Making  of  a  Mechanical  Optician 


155 


There  are  many  styles  of  soldering  blocks,  such  as  charcoal, 
asbestos  and  numberless  patented  ones.  Webster's  soldering  block 
(Fig  170)  is  the  best  and  this,  with  a  charcoal  block,  is  all  that 
is  necessary.     A. borax  slate  (Fig.  17O  will  be  needed  and  this 


Fig.  169 


is  a  slate  having  a  concavity  in  which  bora.x  and  water  is  mixed. 
The  borax  is  prepared  in  tinfoil  and  can  be  used  in  the  wrapper, 
so  that  it  does  not  soil  the  fingers.  In  using  put  a  few  drops  of 
water  on  the  slate  and  rub  the  borax  around  a  few  times  until 
the  water  looks  milky.  It  is  then  applied  with  a  small  camel's  hair 
brush.     Two  jars  will  be  required,  one  containing  a  solution  of 


Fig.    170 — Webster's   soldering  block 


one  part  sulphuric  acid  and  two  parts  water.  After  the  metal 
is  heated  in  soldering  it  is  blackened  and  if  dipped  in  the  acid, 
while  hot,  this  is  removed.    It  is  then  rinsed  in  plain  water. 

These  few  articles  are  all  that  is  required  for  the  soldering, 
with  the  exception  of  solder.     This  can  be  obtained  in  several 


156 


The  Making  of  a  Mechanical  Ol'ticiaii 


forms.  The  most  common  is  silver,  or  hard  solder.  It  is  sold  in 
flat  strips,  which  can  be  cut  with  scissors  into  small  bits,  or  it 
can  be  had  all  cut  as  small  as  desired. 

Although  silver  solder  will  answer  all  purposes  a  great  many 
use  sold  solder.    This  can  be  obtained  in  all  karats  and  is  usuallv 


Fig.    171 — Borax    slate 

claimed  to  be  "easy  flowing."'    A  spool  of  soft  solder  is  handy  to 

have  around,  but  it  should  never  be  used  in  repairing  spectacles. 

For  tools  one  will  need  all  the  ordinary  pliers,  such  as  flat, 

round  and  snipe-nose;  also  the  hollow-chop  and  cutting  pliers.     It 


Fig.    172 — Spectacle   and   eyeglass  stake 

will  also  be  necessary  to  have  two  or  three  pairs  of  tweezers ;  one 
should  be  a  good  pair  for  picking  up  screws,  etc.,  but  the  others 
can  be  cheap  ones.  The  latter  should  have  a  slide  so  that  they 
can  be  used  to  hold  articles  while  soldering.  As  it  is  necessary 
to  blow  the  flame  on  the  points,  it  draws  the  temper  so  that  they 
are  of  no  use  for  any  other  purpose.    A  pin  vise  should  be  added 


The  Making  of  a  Mechanical  Optician  157 

for  holding  wire,  etc.  This  is  especially  handy  when  filing  down 
wire  for  rivets  and  things  of  that  kind.  A  small  vise  should  be 
screwed  to  the  bench  and  a  small  anvil  that  stands  on  the  bench 
will  be  found  very  convenient.  A  good  assortment  of  screw- 
drivers should  be  selected ;  a  good,  substantial  one  with  a  wood 
handle  and  two  or  three  others  with  different  size  blades  and  with 
swivel  tops.  A  spectacle  and  eyeglass  stake  (Fig.  1/2)  is  very 
good  to  hold  the  endpieces  of  frames  when  extracting  old  screws. 
This  is  made  with  a  wood  base  to  stand  on  the  bench,  or  it  can 
be  had  for  a  vise.  There  are  also  a  number  of  screw  extractors 
on  the  market,  but  one  of  the  spring  punches  fitted  with  a  screw 
extractor  is  al]  right  (  Fig.  173  ).  A  couple  of  small  hammers  will 
be  needed,  and  have  one  with  a  brass  head.  This  will  not  mar 
or  dent  some  of  the  softer  metals  as  easily  as  steel. 

A  good  assortment  of  files  is  required — rat  tail  in  one  or 


Fig.   173 

two  sizes ;  a  flat  one  four  or  five  inches  long  and  five-eighths 
of  an  inch  wide;  a  three  and  a  half  or  four-inch  half  round;  a 
square  file,  not  too  large ;  also  a  screw  head  file.  For  the  cut, 
do  not  have  them  too  coarse.  If  you  have  a  good  assortment 
have  them  range  from  Nos.  2  to  6;  No.  4,  however,  is  about  the 
medium  cut.  It  is  well  to  have  all  these  fitted  with  handles,  as 
better  work  can  be  done.  These  can  be  obtained  in  assorted 
sizes  for  about  five  cents  each.  A  burnisher  is  a  good  tool  to 
have,  but  not  too  large  a  one. 

Buff  sticks  will  be  needed ;  also  crocus  and  emery  sticks. 
For  buffing  the  ordinary  felt  stick  is  all  right,  but  for  smoothing 
and  finishing  for  the  buffing  a  leather  stick  is  required.  These 
can  be  bought  with  a  kind  of  rawhide,  quite  thick;  the  stick 
is  also  very  long.     This  should  be  cut  down  so  that  it  is  fairly 


158 


The  Making  of  a  Mechanical  Optician 


thin;  i.  e.,  both  the  stick  and  the  leather.  This  will  give  it  a 
little  spring  and  also  allow  it  to  be  used  in  small  places,  such  as 
under  the  shank  of  the  bridge.  The  material  used  with  this  is 
Tripoli ;  or  pulverized  pumice,  mixed  with  oil,  will  answer.  There 
is,  however,  on  the  market  now  a  prepared  form  of  Tripoli  called 
"Cut  Quick."     This  is  in  more  convenient  form. 

These  sticks  are  used  mostly,  however,  if  one  has  no  power. 
With  power,  wheels  can  be  obtained  to  do  most  of  this  work 


Fig.  174 

much  easier.  There  are  certain  jobs,  however,  where  these 
sticks  will  be  found  very  convenient.  A  buff  head  should  be 
large  enough  to  be  substantial,  so  that  it  will  run  true;  also  that 
the  bearings  will  not  wear  quickly.  If  it  is  too  light,  the  shaft 
will  spring  easily  also.  Another  point  is  that,  if  the  bearings  are 
not  good,  it  cannot  be  run  at  a  very  high  speed  without  rattling, 


and  this  is,  of  course,  very  objectionable.  It  should  be  run  at  a 
speed  of  from  two  to  three  thousand  and,  for  all  kinds  of  work, 
with  the  exception  of  finishing  the  ends  of  screws  in  frameless 
work,  it  should  run  towards  you.  This  is  a  point  that  some 
workmen  do  not  understand.     They  have  outfits  with  one  buff 


The  Making  of  a  Mechanical  Optician 


159 


head  and  this  is,  of  course,  fitted  to  run  toward  you  for  buffing, 
etc.  Now  a  screw  finisher  must  run  left-handed,  or  from  you, 
because  if  it  did  not  it  would  turn  the  screw  out  instead  of  round- 
ing it.  On  the  other  hand,  if  we  run  the  spindle  the  other  way, 
or  from  you,  the  screw  finisher  will  be  running  the  right  way, 
but  the  taper  will  be  threaded  the  wrong  way,  so  that  the  wheels 
will  turn  off  instead  of  tightening. 

It  is  also  the  same  with  the  chuck  and  nut.  These  will  loosen 
so  that  nothing  will  stay  in  them.  The  only  way  to  overcome 
this  is  to  have  a  separate  head  for  the  screw  finisher.  If  one 
does  not  have  power  these  heads  can  be  run  very  successfully 


Fig.  176 

by  foot  power.  The  foot  wheel  is  better  than  the  treadle,  as 
more  power  and  speed  can  be  obtained.  There  are  outfits  all 
complete,  however,  with  a  zinc-lined  box  and  treadle  all  belted 
if  desired.  By  purchasing  an  ordinary  buff  head  and  screwing 
to  a  bench,  then  placing  the  foot  wheel  beneath,  is  very  satis- 
factory. 

For  wheels,  get  a  number  of  stiff  brushes  (Fig.  174),  having 
one  each  of  one,  two,  three  and  four  rows.  These  are  used  for 
cutting,  as  well  as  cleaning.  Then  a  felt  buff  wheel  from  three 
to  four  inches  diameter  (Fig.  175),  a  cotton  wheel  about  three 
inches  diameter,  and  also  a  rag  wheel  six  to  eight  inches  diameter 
(Fig.  176).     Rag  wheels  come  thin,  so  three  to  four  will  be  re- 


i6o  The  Making  of  a  Mechanical  Optician 

quired.  Tiiese  should  be  placed  together,  with  cardboard  washers 
on  either  side,  about  two  inches  diameter,  in  place  on  the  buff 
next  the  chuck  and  screw  the  nut  up  tightly.  With  this  kind  of 
a  wheel  better  results  can  be  obtained  in  fine  polishing,  such  as 
putting  on  the  final  finish  on  a  frame.  Care  must  be  used  in 
polishing  on  this  wheel,  however,  as  temples  and  such  things 
catch  very  easily  if  not  held  right.  (This  work  will  be  explained 
in  the  next  article.) 

For  other  small  articles  we  would  suggest  a  hand  or  jeweler's 
brush ;  a  roll  of  binding  wire — i.  c.,  soft  iron  wire,  very  small,  for 
holding  parts  together  while  soldering;  a  stick  of  polishing  rouge 
• — get  the  kind  wrapped  up  in  tin  foils  so  that  you  need  not  get 
any  more  on  the  fingers  than  possible ;  a  solder  burr  for  burring 
out  the  eye  wire  after  soldering;  a  temple  burr  for  end  pieces; 
a  bottle  of  soldering  fluid. 

The  completeness  of  the  outfit  depends,  however,  on  what 
extent  you  intend  to  go  into  repairing.  Years  ago  it  was  neces- 
sary to  be  fitted  to  do  anything,  from  a  simple  solder  to  making 
a  frame  complete,  but  to-day  it  is  entirely  different,  the  goods 
cost  less,  are  made  better  and  a  greater  assortment  of  bridges 
can  be  kept  in  stock.  Consequently,  when  an  old  frame  is 
brought  in  for  repairs  it  is  often  cheaper  to  give  them  a  new 
one,  or  a  new  part,  rather  than  attempt  to  repair  it. 


CHAPTER  X\"I 

SOLDERING  AND  REPAIRING— Continued 

Now  as  to  the  first  step  in  preparing  the  break  to  be  soldered. 
We  will  take,  for  instance,  a  break  in  the  eye  wire.  First  take  a 
fine  file,  a  half-round  is  the  best,  as  it  is  pointed  and  f^'rly  thin. 
It  should  be  very  fine;  No.  6  is  the  best.  With  this  file  lightly 
over  both  sides,  or,  in  other  words,  the  parts  to  be  exposed  to 
the  flame  Then  place  it  on  the  soldering  block  and  secure  it 
with  the  clamps,  so  the  ends  just  come  together.  Now  mix  the 
borax  in  the  slate,  first  putting  a  few  drops  of  water  in  the  bottom, 
and  then  rub  the  borax  around  a  few  times,  until  you  have  ob- 
tained a  milky  fluid.  Then,  with  a  camel's  hair  brush  p  ace  a  little 
on  the  parts  to  be  soldered  and  apply  a  small  piece  of  solder  on 
one  side  of  the  break  and  you  are  ready  to  apply  the  heat,  iurn 
on  the  gas  so  the  flame  will  be  about  two  inches  high. 

If  you  are  using  the  ordinary  gas  bracket,  the  tip  having 
been  removed,  swing  it  directly  in  front  of  you  and  hold  the  blow- 
pipe in  the  right  hand.  The  soldering  block  hold  m  the  le  t, 
at  the  side  of  the  flame.  Now  place  the  blowpipe  side  of  the 
flame  close  to  the  outlet  and  blow  a  small,  steady  blue  flame 
at  the  break  (Fig.  ^77)-  This  flame  should  be  like  a  needle 
point,  holding  the  work  so  the  point  that  touches  the  frame  will 
be  about  %  inch  in  thickness.  Heat  the  part  on  which  the  solder 
is  placed,  and  as  soon  as  the  solder  begins  to  flow  throw  the 
heat  on  the  opposite  side  of  the  break,  thus  drawing  the  solder 

with  the  heat.  ■       ,        i 

H  the  work  is  hehl  in  the  hands,  the  borax  is  placed  on 
l,oth  sides  and  the  solder  on  one  side,  as  before.  Apply  the  heat 
to  the  side  on  which  the  solder  is  placed,  separating  the  parts 
until  the  solder  is  ready  to  flow.  As  soon  as  the  solder  starts 
to  flow,  dip  both  end  of  the  break  in  the  borax  and  apply  the  heat 
on  the  opposite  side,  as  stated  above. 

The  cause  of  melting  is  blowing  too  much  heat,  either  with 
too  large  a  flange  or  blowing  too  long.  Remember  that  it 
require;  but   a   very   small   point   of   flame   and   little  heat,   but 

IGl 


1 62 


The  Making  of  a  Mechanical  Optician 


properly  placed.  If  a  blowpipe  is  used  as  described  in  the  pre- 
ceding article,  it  will  be  found  much  more  convenient,  as  it  can 
be  held  in  any  position.  The  soldering  block  can  be  held  in 
the  left  hand,  or  laid  on  the  bench,  and  the  blowpipe  in  the  right 
and  the  flame  directed  as  desired.  As  soon  as  the  solder  flows 
and  the  eye  wire  seems  to  be  connected,  blow  the  flame  all  over 
the  eye  wire  adjacent  to  the  break  for  a  second,  to  warm  it,  and 
then  plunge  it  into  the  acid,  and  rinse  in  plain  water.  This 
will  remove  all  the  black  and  leave  the  frame  in  good  condition. 
If  for  any  reason  the  parts  did  not  unite,  it  will  be  necessary 
to  start  all  over  frorn  the  beginning.    Do  not  attempt  to  add  more 


Fig.  177 

solder  and  keep  blowing  at  it,  for  this  may  cause  the  frame  to 
melt.    File  the  parts  again,  put  on  more  borax  and  start  again. 

After  the  eye  wire  is  soldered  satisfactorily  it  will  be  neces- 
sar}'  to  file  the  break  a  little  to  smooth  it,  using,  of  course,  the 
fine,  or  No.  6,  cut.  Then  take  the  leather  stick,  referred  to  in  the 
preceding  article,  and  with  tripoli,  pumice  and  oil  or  Cut  Quick, 
which  is  the  prepared  cutting  material,  go  over  the  parts  until 
all  traces  of  file  marks  are  removed.  If  power  is  used,  the  brush 
is  the  proper  wheel  and  the  cutting  material  is  rubbed  on  by 
holding  the  stick  against  the  wheel.  Then  with  a  solder  burr, 
especially  constructed   for  eye  wire,  burr  out  the  inside  of  the 


The  Making  of  a  Mechanical  Optician  163 

eye  wire.     This  little  tool  is  used  in  the  buff  head  and  run  at  a 
fairly  high  speed,  say  about  2000  revolutions  per  minute. 

You  are  now  ready  to  polish.  For  this  work  use  the  cotton 
buff  and  this,  of  course,  runs  toward  you.  Rub  plenty  of  the 
stick  rouge  into  it  while  it  is  running.  Now  hold  the  frame 
tightly  in  both  hands,  with  the  eyes  perpendicular,  and  the  eye 
that  has  been  soldered  downward.  In  this  manner  there  is  no 
way  for  the  frame  to  catch,  provided  you  keep  your  mind  on  it. 
You  will  soon  learn  to  protect  the  parts  that  are  liable  to  catch 
with  the  hands,  such  as  the  end  pieces  and  bridge.  In  all  repair- 
ing it  is  best  to  remove  the  temples,  as  they  are  very  liable  to  get 
in  the  way  of  the  flame  or  catch  in  the  wheel  when  buffing. 
After  the  frame  is  polished  in  good  shape  it  should  be  washed 
with  hot  water  and  soap  to  remove  all  the  dirt  and  rouge  that 
collects  in  the  joints.  When  replacing  the  lens  it  will  be  necessary 
to  reduce  it  a  little,  as  the  eye  is  always  made  a  little  smaller 
when  soldered. 

Most  all  solder  jobs  can  be  done  without  a  soldering  block 
if  one  is  experienced,  but  quite  a  little  practice  is  required.  In 
this  way  the  parts  are  held  together  with  soft  iron  wire,  called 
binding  wire. 

Bridges  can  be  obtained  all  ready  to  solder  to  the  frame; 
that  is,  they  are  bent  and  grooved  for  the  eye  wire.  The  most 
common  method  to-day,  however,  is  to  use  what  is  called  unbent 
bridges.  These  consist  of  the  bridge  stock  in  assorted  lengths, 
tapered  about  one  the  right  size  and  thickness  for  the  shank.  In 
using  this  stock  the  principal  feature  lies  in  judging  the  length 
required.  The  medium  sizes  require  2^^  to  2%  inches.  First 
bend  the  crest  or  arch ;  this  can  be  done  over  the  handle  of  a  tool 
or  any  round  piece  of  wood.  It  is  better  to  do  it  in  this  way 
than  to  attempt  it  with  the  hollow  chop  or  periscopic  pliers,  as 
these  dent  the  stock  and  must  be  taken  out  afterward.  In  gold 
filled  this  is  impossible,  as  the  gold  will  be  finished  too  thin. 
After  the  arch  is  formed,  bend  up  the  shanks.  These  may 
possibly  be  too  long  and  should  be  cut  off,  allowing  stock  enough, 
of  course,  for  the  feet.  A  frameless  bridge  can  be  soldered 
on  straight,  and  if  preferred  the  frame  can  be  made  this  way 
also.  This  style,  when  made  at  the  factory,  however,  has  a  de- 
pression pressed  in  the  eye  wire  to  make  a  blind  joint.  In  repair 
work  this  is  not  attempted. 


164  The  Making  of  a  Mechanical  Optician 

The  bending  of  the  feet  can  best  be  done  in  a  vise,  as  the 
f^tock  must  be  turned  edgewise,  this  being  quite  difficult.  After 
the  feet  are  bent  they  should  be  grooved  with  a  float  file ;  that  is, 
one  with  rounded  edges,  just  the  right  size  for  the  eye  wire. 
You  are  now  ready  to  solder  it  to  the  frame.  First  prepare  the 
eye  wire  by  filing  it  lightly,  the  same  as  for  any  solder.  It  can 
then  be  placed  on  the  soldering  block,  clamped  in  and  the  solder 
placed  on  the  top  of  the  foot  of  the  bridge  (Fig.  178).  This 
operation  can  be  done  better  in  the  hand,  however.  The  eye 
wire  can  be  held  by  the  joint  in  the  left  hand,  and  the  bridge 
in  a  pair  of  tweezers  in  the  right  hand.  By  having  a  slide  on  the 
tweezers,  as  before  described,  it  is  much  easier.  If  the  blowpipe 
is  arranged  so  that  it  can  stand  on  the  bench,  both  hands  will  be 
free  to  work  with. 

Another  method  is  to  use  binding  wire  to  hold  the  parts  in 
position.  In  soldering  the  procedure  is  the  same  as  before,  plac- 
ing the  borax  and  solder  on  the  parts  and  heating  them  and  as 
soon  as  the  solder  begins  to  flow,  throw  the  heat  in  the  direction 
you  wish  the  solder  to  flow.  Just  enough  solder  must  be  used  so 
that  it  will  flow  freely  in  the  groove  in  the  bridge,  but  it  is  un- 
necessary to  have  so  much  that  it  will  flow  outside  all  over  the 
joint.  Care  must  also  be  used  to  see  that  the  bridge  is  in  the 
center  of  the  eye  wire.  When  one  eye  is  soldered,  the  other  can 
be  put  on  the  same  way.  The  frame  can  then  be  lined  up  and 
the  bridge  bent  to  dimensions. 

At  this  point  it  is  well  to  see  that  the  crest  is  the  desired 
angle.  If  not,  it  can  be  formed  with  a  pair  of  crest-angling 
pliers.  If  one  does  not  have  this  tool  the  angle  must  be  made 
first,  while  the  stock  is  straight.  For  all  saddle  bridges,  except 
the  lowest  ones,  such  as  no  height,  the  natural  bend  of  the  stock 
produces  about  45°.  "C"  bridges,  however,  must  be  bent  first. 
This  operation  is  done  by  tilting  the  stock  edgewise  a  little.  This 
can  be  done  by  holding  both  ends  of  the  stock  securely  with 
pliers  and  bending  it  over  the  edge  of  the  bench  pin.  After  the 
dimensions  are  made  right  any  superfluous  solder  can  be  filed 
oflf  with  a  fine  file  and  finished  with  the  buff  stick  and  Cut  Quick. 

With  power  this  can  be  done  much  better  and  quicker.  For 
this  work  use  the  brush  wheel,  putting  on  plenty  of  the  cutting 
material.     This  wheel  reaches  in  under  the  shank  and  smooths 


The  Making  of  a  Mechanical  Optician 


165 


up  the  foot  very  nicely.  After  smoothing  up  in  good  shape  it 
can  be  poHshed  in  the  regular  way,  being  very  careful,  however, 
to  hold  the  frame  tightly,  so  that  the  shank  will  not  catch  in  wheel. 
One  of  the  most  common  breaks  is  in  the  shank,  at  the  turn. 
Formerly  this  was  considered  an  unsatisfactory  job,  as,  in  order 
to  make  it  strong,  quite  a  little  solder  must  be  left  in  the  turn. 
This  was  objectionable  and  yet,  if  finished  in  good  shape,  it  made 
a  very  weak  joint,  as  considerable  strain  comes  at  this  point. 
Now   this    is   a    very    common    job,   however,    but    the    practice 


Fig.  178 

generally  is  to  leave  plenty  of  solder;  in  fact,  sometimes  it  is 
pretty  well  filled  up.  For  this  operation  it  is  best  to  use  binding 
wire,  so  as  to  bring  the  parts  together  in  the  right  position.  The 
parts  must  be  prepared  in  the  same  manner  as  before  prescribed 
and  proceed  in  the  same  manner. 

First  prepare  the  eye  wire  by  filing,  then  groove  out  the  end 
piece,  unless  possibly  it  has  just  pulled  out.  Most  breaks  of  this 
kind,  however,  are  next  to  the  end  piece,  so  that  a  part  of  the 
eye  wire  is  in  the  joint.  When  doing  a  job  of  this  kind,  be  sure 
and  remove  the  temple  and  screw  and  separate  the  joints.  Do 
not,  under  any  circumstances,  attempt  to  solder  an  end  piece 
on  the  eye  wire,  having  them  screwed  together,  for  if  you  do  you 
will  find  both  end  pieces  soldered  together  and  it  will  be  like  one 
mass,  and  it  can  never  be  taken  apart.     For  this  operation  the 


l66  The  Making  of  a  Mechanical  Optician 

end  piece  can  be  bound  to  the  eye  wire  with  binding  wire,  and  in 
this  case  wind  it  around  the  eye  wire  several  times,  quite  a  little 
distance  back  from  the  joint,  and  insert  the  other  end  through 
the  screw  hole  and  place  it  on  the  end  of  the  eye  wire.  Do  not 
attempt  to  bind  it  so  that  the  eye  wire  comes  near  the  solder.  A 
simple  way  to  do  this  work  is  to  hold  the  frame  in  one  hand  and 
hold  the  joint  on  an  old  file,  by  inserting  it  in  the  screw  hole.  Do 
not  use  much  solder  in  this  operation,  as  it  requires  but  the 
smallest  piece  to  hold  it  securely.  After  the  joint  is  soldered  it 
will  be  necessary  to  burr  out  the  eye  wire  and  possibly  reduce 
the  lens  a  trifle. 

This  material  is  worked  the  same  as  gold,  except  that  one 
must  bear  in  mind  that  there  is  only  a  very  thin  coating  of  gold 
over  the  base  metal.  One  stroke  of  the  file  will  cut  through  it, 
consequently  the  work  must  be  done  in  such  a  manner  that  no 
filing  is  necessary.  The  great  feature  in  handling  gold  filled  is 
to  use  the  smallest  amount  of  solder  possible.  In  this  way  it 
flows  only  into  the  break  or  between  the  joints.  At  the  factory 
this  work  is  usually  covered  with  a  coating  of  boracic  acid  to 
prevent  discoloring.  This  is  a  powder  and  by  wetting  the  frame 
and  placing  it  in  the  powder  enough  will  stick  to  it.  The  polishing 
should  be  done  as  quickly  as  possible,  as  the  metal  will  not  stand 
too  much. 

Temples  are  very  unsatisfactory  to  repair  and  only  in  cases 
of  emergency  should  it  be  attempted.  They  are  made  in  gold 
by  drawing,  and  in  gold  filled  by  swedging.  This  process  gives 
them  the  temper  and  spring.  As  soon  as  heat  is  applied  to  them 
they  are  annealed,  and  consequently  are  very  soft.  The  best 
way  to  repair  them  is  to  use  a  ferrule.  These  are  small  pieces 
of  tubing  just  the  right  size  to  slip  over  the  broken  ends,  and 
as  the  base  metal  is  solder  it  is  only  necessary  to  apply  the  heat 
and  a  good  joint  is  obtained.  This  method  leaves  a  bunch  on  the 
temple,  but  it  is  fairly  strong. 

Spring  stock  must  have  considerable  temper  and  spring,  con- 
sequently when  heat  is  applied  they  are  practically  useless.  When 
one  is  broken  near  the  end,  or  screw  hole,  a  new  hole  can  be 
punched,  and  although  it  makes  it  somewhat  shorter  it  is  very 
satisfactory.  This  is  the  only  way  any  kind  of  a  spring  can  be 
repaired,  but  even  this  method  hardly  pays,  as  springs  can  be 
obtained  at  a  very  low  price. 


CHAPTER  XVII 


SOLDERING  AND  REPAIRING — Continued 

Steel  goods  are  fast  disappearing,  although  the  better  class 
of  trade  still  call  for  them  occasionally,  preferring  to  wear  them 
instead  of  gold.  It  seldom,  if  ever,  pays  to  repair  them,  unless 
possibly  it  is  to  solder  on  an  end  piece.  Steel  is  handled  in  much 
the  same  manner  as  gold,  except,  of  course,  silver  solder  is  always 
used.  The  parts  to  be  soldered  are  first  filed  bright,  so  that  all 
traces  of  rust  or  foreign  substances  are  removed.  The  parts  are 
then  dipped  in  borax  and  the  heat  and  solder  applied  as  described 
in  the  preceding  article.  This  metal  must  be  heated  to  a  greater 
temperature;  in  other  words,  red  hot.  It  is  then  plunged  in  the 
acid  and  this  removes  the  black  and  also  restores  the  temper  to 
a  certain  extent.  In  finishing,  the  surplus  solder  is  filed  away 
and  smoothed.  The  frame  then  should  be  rubbed  with  fine  emery 
cloth  to  leave  the  steel  bright.  If  it  is  to  be  nickeled,  no  more 
finishing  is  required.  If  the  finish  is  bronze  or  blue  it  must  be 
refinished  to  match  as  near  as  possible  the  old  finish. 

At  the  factory  the  process  is  simplified  by  using  hot  sand. 
This  produces  an  even  color  of  any  shade  desired.  For  small 
shops  it  is  hardly  practical  to  attempt  this  method,  as  it  is  so 
seldom  used.  The  easiest  way  is  to  use  an  alcohol  lamp  (gas  will 
not  answer,  as  the  regular  flame  will  blacken  the  work  and  a 
Bunsen  burner  has  too  much  pressure).  When  using  the  ordinary 
jewelers'  alcohol  lamp  the  wick  should  be  pressed  down  so  that 
a  very  small  flame  is  obtained.  The  frame  is  then  held  in  the 
left  hand  and  the  lamp  in  the  right.  Take  the  work  to  a  place 
where  good  daylight  can  be  obtained,  as  artificial  light  will  not 
answer  and  neither  will  poor  daylight  produce  satisfactory 
results.  Now  apply  the  flame  directly  to  the  metal  (Fig.  179) 
and  then  remove  it  quickly  so  that  it  is  heated  but  a  very  little. 
Repeat  the  operation  several  times,  being  careful  to  heat  the 
frame  but  a  second  at  a  time.  The  color  will  be  observed  after 
the  flame  is  removed  and  it  will  be  noticed  that  it  changes  con- 
siderably in  a  second  or  two.  Bronze  will  appear  first,  then  blue, 
and,  if  you  are  not  careful,  you  will  burn  it  and  bright  spots  will 
appear.    As  soon  as  each  spot  is  the  desired  color  move  the  flame 


i68  The  Mak'uuj  of  a  Mechanical  Optician 

along.  Tliis  is  one  of  the  most  difficult  jobs  in  repairing,  and,  to 
produce  an  even  color,  it  requires  considerable  practice.  If  the 
color  gets  too  deep  refinish  the  frame  with  emery  cloth  and  try 
again. 

We  are  frequently  called  upon  to  cut  a  frame  to  fit  old 
lenses.  In  this  work  all  four  end  pieces,  if  it  is  a  spectacle,  must 
be  moved.  This  requires  four  solders,  so  it  is  easily  seen  why  this 
work  is  expensive.  If  one  end  piece  on  each  side  is  moved  the 
frame  will  be  out  of  shape.  Take  one  end  piece  at  a  time,  blow 
the  heat  on  to  remove  it,  then  refinish  it  and  set  it  back  on  the 
eye  wire  slightly.  The  end  that  overlaps  can  then  be  filed  ofif 
square.     There  are  lens  washers  now  on  the  market  which  are 


Fig.  179 

used  extensively  for  this  purpose  and  these  are  very  satisfactory 
(Fig.  ISC').  If  they  are  not  at  hand,  tinfoils,  or,  better  still,  tea 
lead,  can  be  inserted  in  the  eye  wire  to  fill  the  open  space.  If 
the  lens  is  only  a  very  little  loose,  the  end  pieces  can  be  filed 
slightly,  but  this  method  reduces  the  thickness  so  that  it  weakens 
the  joints  considerably.  It  is  always  preferable  to  fit  new  lenses 
if  possible  and  this  can  frequently  be  done  without  the  customer's 
knowledge. 

Screws  for  all  standard  frames  can  be  obtained  cheaply  so 
that  it  is  well  to  have  a  good  supply  on  hand.  If  one  has  taps 
for  these  threads  they  can  be  used  to  replace  odd  makes  by  simply 
tapping  new  threads  (Fig.  i8i  ).  The  great  difficult)-  is  in 
removing  the  old  screw,  however.  For  most  jobs  the  screw 
extractor,  referred  to  on  page  157,  will  suffice.  This  can  be 
used  for  end-piece  screws  if  the  head  is  not  too  far  gone.     If 


The  Making  of  a  Mechanical  Optician  169 

the  head  has  been  turned  off  completely  it  will  probably  be 
necessary  to  drill  it  out.  Small  twist  drills,  such  as  can  be 
purchased  in  any  hardware  store,  are  used  for  this  purpose. 
After  the  screw  is  drilled  out  the  hole  must  be  tapped  and  the 
new  screw  inserted.     If  the  ends  protrude  they  should  be  filed 


Fig.  180 


oH  carefully  and  the  end  piece  polished.  Stud  screws,  or  screws 
that  project,  can  frequently  be  removed  successfully  by  filing  a 
slot  in  the  head  with  a  screw  head  file.  By  then  placing  the 
frame  in  a  stake  (Chapter  X)  or  against  a  solid  square  surface 
(if  a  stud  screw  hold  it  with  a  pair  of  stud  or  round-nose  pliers) 
and  by  using  a  wooden  handle  screwdriver  it  can  be  turned 
gradually. 

Fingerpiece  mountings  are  used  so  extensively  at  the  present 
time  that  it  is  well  to  be  prepared  to  fit  these  while  the  customer 
waits.  The  factories  will  possibly  replace  these  without  charge, 
but  it  seems  absurd  to  require  a  customer  to  go  without  their 
glasses  for  from  one  to  three  days  when  these  can  be  inserted 
in   a   few  moments.     These   springs   can  be   obtained    from   the 


Fig.  181 

jobbers  in  gold  filled  for  seventy-five  cents  a  dozen  pair  and  in 
gold  for  a  dollar  and  a  half.  They  come  in  rights  and  lefts  and 
with  two,  three  and  four  coils.  The  best  mountings  have  four 
coils,  as  this  produces  an  easier  pressure  and  less  liable  to  break. 
They  are  placed  on  the  screw  with  the  top  ends  over  the  inside 
edge  of  the  straps,  the  coil  being  wound  from  left  to  right  on  the 
right  side  and  from  right  to  left  on  the  left  side  (Fig.  182.  )  The 
lower  end  is  turned  under  the  guard.  After  both  ends  are  bent 
so  they  are  secure  they  can  be  cut  of?  fairly  close,  as  will  be 
readily  seen. 

There    is    another    fingerpiece    mounting    that    works    on    a 


i-o  The  Making  of  a  Mechanical  Optician 

principle  different  from  the  coil  or  spiral  spring  mountings.  The 
spring  of  this  mounting,  instead  of  being  attached  to  the  bridge, 
is  attached  on  the  arm  of  the  guard  (Fig.  183)  and  near  the 
g^ard.  If  it  is  desired  to  increase  or  decrease  the  tension  of  the 
spring  on  this  mounting  the  entire  guard,  including  the  spring, 
may  be  removed  and  the  arm  or  lever  of  the  spring  (not  the 
arm  of  the  guard)  may  be  curved  slightly  or  straightened.  Curv- 
ing the  lever  toward  B  increases  the  tension  and  straightening 
toward  A  decreases  the  tension. 

In  case  the  arms  of  the  guards  are  broken  on  any  style  of 
fingerpiece  mounting  it  is  far  better  to  replace  them  with  an  en- 
tirely new  guard,  as  soldering  is  always  unsatisfactory  and  is  far 
from  neat  in  appearance. 

It  is  frequently  necessary  to  fit  new  zylonite  to  guards,  al- 


Fig.    1S2 — Illustration   showing    position    of   right   and    left    coil    springs 
in  their  relation  to   the  mounting 

though  it  hardly  pays,  except  on  gold.  There  are  a  great  many 
styles  where  the  zylonite  is  peculiar  in  shape,  and  at  the  factories 
these  are  punched  out  with  dies.  When  one  is  called  upon  to 
furnish  one  of  the  irregular  shape  the  best  that  can  be  done  is 
to  cut  it  with  shears  or  a  knife  as  near  as  possible.  This  material 
can  be  smoothed  and  shaped  wth  a  file  so  that  it  is  possible  to  do 
a  very  good  job.  Zylonite  can  be  obtained  in  any  form,  such  as 
plain  sheets,  plain  strips  or  in  pieces  ready  to  be  fitted.  The  cor- 
rugations are  pressed  in  at  the  factories,  so  it  can  be  obtained  in 
this  form  if  preferred.  It  is  well  to  have  a  small  assortment, 
however,  so  that  all  sizes  can  be  obtained.  Small  wire,  or  even 
common  pins,  are  used  to  secure  it  to  the  guard,  but  rivets,  made 
especially  for  this  purpose,  should  be  kept  on  hand.  The  guard  is 
already  punched  and  small  holes  should  be  made  in  the  zylonite 
just  large  enough  to  force  the  pins  through.  These  are  driven 
through  from  the  back  and  are  then  cut  of¥  quite  close  and  with  a 


The  Making  of  a  Mechanical  Optician 


171 


light  hammer  riveted  gently.  If  the  holes  are  just  the  right  size 
it  requires  but  a  few  taps.  If  plain  zylonite  is  used,  it  will  be 
necessary  to  corrugate  it  with  a  screw  head  file,  making  the  cuts 
as  small  and  as  regular  as  possible.  Scraps  of  shell  can  also  be 
used  for  this  purpose. 

Corks  have  to  be  fitted  quite  frequently,  although  many  times, 
if  they  are  only  soiled,  they  can  be  washed  with  soap  and  water. 
This  is  the  method  employed  when  guards  are  slightly  soiled 
from  lying  in  stock.  If  they  are  quite  bad  and  not  worn  down 
they  can  be  sandpapered  to  look  as  good  as  new.     For  this  pur- 


Fig.  183 


Fig.  184 


pose  No.  GO  sandpaper  is  used,  any  grade  coarser  than  that  will 
rough  them.  Cork  can  be  obtained  in  the  rough,  cut  the  right 
size,  or  it  can  be  had  all  rounded  and  finished  with  groove,  ready 
to  fit  into  the  guard.  The  difference  in  price  is  so  slight  that  it 
is  better  to  use  the  finished.  The  old  cork  should  be  removed 
and  the  edges  of  the  guard  lifted  with  a  burnisher  or  a  knife  just 
enough  so  that  the  cork  will  slide  into  the  guard  easily.  The 
edges  can  then  be  burnished  down  so  that  it  will  hold  securely. 
The  end  can  then  be  trimmed  off  and  if  the  guard  is  then  too 
thick  it  can  be  sandpapered  down.  Some  styles,  such  as  No.  o 
Anchor  (  Fig.  1S4),  have  a  round  disk  which  must  be  riveted  and 
for  any  of  these  styles  the  disks  can  be  ordered,  cut  to  shape.  The 
regular  styles  of  guards  in  nickel  and  gold  filled  are  low-priced, 
so  that  it  is  often  cheaper  to  fit  new  ones  than  the  charge 
made  to  cover  the  cost. 

Dowels,  or  rivets,-  as  they  are  more  generally  called,  have 


172  The  Making  of  a  Mechanical  Optician 

to  be  fitted  to  spectacle  end  pieces.  In  gold  filled  they  loosen 
and  fall  out  easily.  In  gold  they  wear  so  that  the  temples  are 
loose  and  must  be  replaced.  The  only  satisfactory  way  to  tighten 
old  gold  temples  is  to  fit  new  dowels,  but  for  qiiick  repairs  spec 
washers  can  be  obtained.  Two,  three,  or  as  many  as  are  necessary, 
are  placed  on  the  dowel  to  fill  up  the  space  in  the  joint  and  the 
end  piece  screwed  together.  Dowels  can  be  obtained  in  the 
different  sizes  ready  for  use.  They  are  tapered  and  left  long  so 
that  they  will  fit  any  joint.  When  fitting  these,  it  is  only  necessary 
to  drive  out  the  old  one  and  insert  the  new.  Place  the  joint 
on  an  anvil  or  vise  so  that  the  small  end  of  the  dowel  can  be 
driven  into  a  hole  and  with  a  light  hammer  tap  it  lightly  a 
few  times  and  then  try  the  temple.  If  it  is  not  fairly  tight, 
drive  it  in  a  little  farther.  If  it  is  still  loose  drive  it  out 
again  and  with  a  small  broach  ream  out  the  hole  a  little.  The 
dowel  can  then  be  inserted  and  driven  in  slightly.  Do  not 
have  the  temple  fit  too  snug  but  see  that  it  works  fairly  stiff. 
If  it  works  too  freely  it  may  be  too  loose  after  the  ends  of 
the  dowel  are  finished  off  and  it  will  then  be  necessary  to  do 
the  work  all  over  again.  When  the  dowel  is  in  place  the  ends 
should  be  cut  off  closely  and  finished  first  with  a  fine  file  and  then 
polished  on  the  buff  wheel.  If  the  finished  dowels  are  not 
available,  steel  wire  can  be  used,  a  size  a  little  larger  than  the  hole 
should  be  selected  and  a  piece  about  a  half  an  inch  long  cut  off. 
This  should  be  placed  in  a  pin  vise  and  filed  to  a  slight  taper. 


Fig.   185 

It  can  be  done  on  the  bench  pin,  revolving  it  with  the  left  hand 
and  filing  with  the  right.  In  gold  filled  the  dowels  are  usually 
rounded  on  the  ends  and  for  this  metal  the  finished  dowels  for  the 
particular  grade  that  you  are  using  should  be  kept  in  stock.  A 
regular  dowel  can  be  used,  however,  and  the  ends  rounded  with 
a  screw  finisher.    As  gold  filled  is  a  softer  metal  the  temples  are 


The  Making  of  a  Meclumkal  Optician  173 

fitted  more  loosely  and  the  joint  brought  together  tightly.  This 
may  not  seem  practical,  but  it  is  the  only  way  the  dowels  can  be 
made  to  hold  in  the  end  pieces.  If  they  are  fitted  the  same  as 
gold  the  temple  will  work  them  loose.  In  some  grades  of  gold 
filled  the  flush  dowel  is  used  and  the  largest  end  is  punched 
slightly  with  a  very  small  punch  (Fig.  185).  This  is  supposed 
to  spread  the  head  slightly  to  hold  it  in  place. 

There  are  a  number  of  small  jobs  that  one  is  called  upon  to 
do  that  are  interesting  if  time  is  of  no  account,  such  as  drawing 
out  gold  temples,  or  balling  them.  To  ball  a  gold  temple  it  is 
only  necessary  to  file  the  end  slightly,  to  clean  it  and  then  dip  it 
in  the  borax  and  apply  the  heat.  This  is  very  convenient  when  it 
is  necessary  to  shorten  temples.  Gold  filled  cannot  be  done  in  this 
manner  but  requires  a  gold  ball  soldered  on  the  end.  This  is  a 
little  more  difficult  and  is  not  attempted  unless  necessary. 

The  fitting  of  lorgnette  springs  is  now  quite  common  .and  this 
is  a  job  that  requires  quite  a  little  ingenuity.  The  springs  can  be 
obtained  quite  reasonable  and  if  one  has  the  time  and  cared  to 
e.Kperiment  with  them  a  little  practice  will  enable  them  to  do  as 
good  a  job  as  can  be  done  at  the  factory.  When  fitting  the  center 
springs  to  plated  styles  it  is  necessary  to  have  them  replated. 
Platers  when  doing  this  work  often  use  acid,  which  destroys  the 
spring,  so  they  should  be  cautioned  regarding  this  point.  The 
older  styles,  such  as  heirlooms,  are  very  difficult  to  repair  and 
should  not  be  attempted. 

INSPECTING  A  PRESCRIPTION   (THE  LENSES) 

The  inspection  of  a  completed  prescription  calls  for  more 
than  a  mere  glance  and,  even  though  scrutinized  carefully,  there 
is  much  more  to  be  done.  After  the  workman  in  a  large  shop  has 
mounted  a  spectacle  or  eyeglass  he  does  not  attempt  to  straighten 
or  "true  it  up,"  but  it  is  passed  along  to  a  truer  or  inspector.  If 
the  shop  is  large  enough  for  a  truer,  the  work  will  pass  through 
his  hands,  and  his  part  is  to  straighten  and  line  up,  or,  in  other 
words,  put  the  glasses  in  shape.  It  is  then  passed  along  to  the 
inspectors,  whose  part  of  the  work  is  to  see  that  the  prescription 
is  filled  correctly  and  to  put  on  the  finishing  touches.  Even 
though  the  truer  may  be  an  expert  workman,  it  is  perhaps  im- 


1/4 


The  Making  of  a  Mechanical  Optician 


possible  for  him  to  allow  each  job  the  necessary  time  and,  con- 
sequently, a  temple  must  be  curved  a  little  more  or  some  other 
little  point  muct  receive  the  attention  of  the  inspector.  In  many 
of  the  large  shops  this  work  is  done  entirely  by  the  inspectors, 
and  with  this  method  the  best  results  are  always  obtained. 

An  inspector  must  necessarily  be  an  expert ;  he  must  not  only 
be  familiar  with  mounting  in  all  its  branches,  but  he  must  have  a 
thorough  knowledge  of  lenses.  To  this  must  be  added  a  good 
education  to  thoroughly  understand  the  different  prescriptions. 
The  reading  of  a  prescription  intelligently  often  requires  quite  a 


Fig.  186 

little  study ;  in  the  first  place,  the  writing  is  not  always  legible, 
and  then  again,  two  different  meanings  can  often  be  interpreted. 
The  work  of  inspecting  should  be  carried  through  systematically, 
for  the  reason  that  if  the  time  is  spent  truing  up  the  mounting 
and  then  a  lens  is  found  to  be  incorrect,  the  work  was  done  for 
nothing.  Each  time  a  lens  is  fitted  the  mounting  is  thrown  out 
of  adjustment,  even  if  only  a  very  little. 

The  first  step  is  to  neutralize  the  lenses :  this  should  be  done 
with  a  spherical  test  case.  Cylinders  should  never  be  used,  as 
they  are  more  awkward  and  necessitate  the  lining  up  of  the  lenses 
first.  With  sphericals  the  spectacle  can  be  held  at  the  proper 
angle,  or  as  near  as  possible,  and  the  lens  neutralized  in  this 
direction.  It  can  then  be  turned  at  right  angles  and  the  opposite 
meridian  tested.     If  preferred,  the  first  test  lens  can  be  held  in 


The  Making  of  a  Mechanical  Optician 


175 


position  and  another  spherical  lens,  with  the  same  focus  as  the 
cylinder  calls  for,  held  over  it.  The  better  way,  however,  is  to 
use  one  for  the  spherical,  then  remove  it,  and  place  one  in  posi- 
tion for  the  other  meridian,  having  the  combined  strength  of  the 
spherical  and  the  cylinder. 


Fig.  187 

For  example,  the  lens  to  be  neutralized  is  -j-  i  3  +  50  ax. 
90°.  First  take  a  —  i  spherical  and  test  the  vertical  meridian; 
then  remove  this  and  select  a  ■ —  1.50  to  neutralize  the  opposite 
meridian.  In  this  operation  no  attention  is  given  to  the  axis, 
except  that  the  glasses  should  be  held  so  that  the  axis  is  approxi- 
mately perpendicular.  The  lens  measure  is  used  by  many  for  this 
work,  and  if  it  is  to  be  relied  on,  must  be  watched  constantly, 
to  see  that  it  does  not  get  out  of  adjustment.  With  constant  use 
the  three  points  gradually  wear,  so  that  new  points  need  to  be 
put  on  occasionally.  This  work  must  be  done  at  the  factory,  but, 
by  testing  it  at  intervals  on  a  plane  prism  and  adjusting  the  center 
pin  it  can  be  kept  in  condition. 

The  next  step  is  to  locate  the  axis  and  mark  it.  This  should 
be  done  on  a  machine  if  possible,  but  if  one  does  not  have  one, 
a  straight  line  drawn  on  a  card  will  answer  for  medium  and 
strong-power  lenses,  and  one  on  the  wall,  at  a  distance,  for  the 
weak   power.      (For  instruction   in  this   work   see   Chapter   III, 


176 


The  Making  of  a  Mechanical  Ol^tician 


"IMarkiiig  Lenses."  This  explains  the  breaking  of  the  hne  and 
the  drawings  show  how  the  axis  can  be  located. )  Three  dots  are 
then  placed  on  the  lens,  one  being  the  center   (  Fig.   186 ) .     The 


Fig.   188 

spectacles  are  then  laid  on  an  axis  chart  (Fig.  187),  with  the 
glass  screws  on  the  180°  line,  and  the  two  dots  on  the  extreme 
edge  will  locate  the  axis. 

A  machine  fiDr  this  purpose  is  the  Standard  centering  ma- 


Fig.  189 

chine  (  Fig.  188).  This  is  equipped  with  a  holding  device  in  which 
the  spectacles  are  placed.  An  axis  dial  on  the  back  can  be  op- 
erated so  that  it  will  revolve.     When  the  spectacles  are  placed 


The  Making  of  a  Mechanical  Opticiai 


^77 


in  position  the  line  will  appear  broken  (Fig.  189  )  :  the  dial  ,s  then 
revolved  until  the  lines  are  continuous  (Fig.  190).  Ihe  axib  is 
then  read  from  the  dial.  For  example,  if  the  lens  was  axis  45 
and  the  machine  happened  to  be  set  at  90°,  the  lines  would  appear 
as  in  1-i-  1S9.  The  advantage  of  a  machine  over  the  method  ot 
holding  "the  glasses  bv  hand  is  that  the  spectacles  are  held  rigidly 
and  the  axis  is  read  quickly  from  the  dial;  it  is  unnecessary  to 
dot  the  lenses  and  then  place  them  on  an  axis  chart.  There  has 
been  a  machine  in  use  bv  a  well-known  retail  house  where  the 
axis  can  be  located  electrically.     It  is  known  as  the  Lloyd  axo- 


Fig.  190 


nometer  (Fig.  191  )  and  is  now  on  the  market.     With  this  ma- 
chine the  axis  can  be  located  both  quickly  and  accurately. 

The  axis  having  been  located,  the  next  step  is  to  inspect  the 
size  and  shape  of  the  lenses.  If  it  is  a  repair  job.  the  new  lens 
must  match  the  old  lens  on  the  opposite  side.  The  size  is  meas- 
ured for  length  and  width  with  a  rule,  and  this  should  be  read  in 
millimeters.  If  the  prescription  calls  for  a  pair  of  00  eye  lenses 
the  measurements  will  be  40  mm.  long  by  31  mm.  wide.  Although 
it  is  perhaps  necessarv  to  measure  both  lenses,  an  experienced 
eve  will  readilv  detect  a  ditiference  in  size  of  the  two  lenses.  This 
can  be  noticed  as  the  shape  of  the  two  are  compared.     If  the 


178 


The  Making  of  a  Mechanical  Optician 


lenses  are  ground  in  an  automatic  machine  they  must,  of  course, 
be  alike,  but  when  ground  by  hand  it  is  a  very  easy  matter  to  get 
one  different  from  the  other.  This  is  especially  true  in  repair 
jobs,  where  a  new  lens  is  ground  to  match  an  old  one.     It  is 


Fig.  191 

possible  to  grind  two  lenses  exactly  the  same  measurements  and 
still  have  a  decidedly  different  oval  (Fig.  192).  This  part  of  the 
work  is  where  the  expert  inspector  counts,  and  many  jobs  are 
rejected  for  this  reason.  With  a  little  practice  the  shape  can 
readily  be  compared  and  at  the  same  time  the  difference  in  the 
size  will  be  noted. 


192 


The  lenses  having  been  found  to  be  the  correct  size  and 
shape,  the  inspector  then  notices  if  the  bevel  on  the  edge  is  about 
right.     If  too  little  bevel  has  been  placed  on  the  edges,  they  will 


1  he  Making  of  a  Mechanical  Optician  179 

chip  easily,  therefore  the  job  must  be  returned  to  the  grinder. 
For  this  operation  it  will  be  necessary  to  take  the  lenses  out,  and 
they,  of  course,  must  be  remounted.  Here  it  will  be  noted  that 
if  the  spectacle  had  been  trued  up  the  time  was  wasted,  and  must 
be  done  over  again.  If  the  bevel  is  too  deep,  or  an  attempt  to 
take  out  a  chip  has  been  made,  thereby  leaving  the  bevel  uneven, 
a  new  lens  must  be  ground.  A  lens  that  has  been  beveled  too 
much  will  spoil  the  appearance  of  any  pair  of  glasses,  as  this 
gives  the  lens  the  appearance  of  having  a  white  edge.  A  good 
illustration  of  this  is  a  pair  of  bevel  edge  or  frame  lenses  mounted 
up  as  a  frameless  spectacle. 

When  inspecting  the  bevel  the  edges  must  be  watched  care- 
fully for  chips.  These  are  often  minute,  but  when  exposed  to  an 
electric  light  will  sometimes  sparkle  like  a  diamond.  In  grinding 
lenses  by  machine,  the  edges  should  come  out  perfectly  clear  and 
as  sharp  as  a  knife  edge,  provided  the  grindstone  is  in  good  con- 
dition. Many  stones  are  neglected,  however,  and  with  constant 
grinding  over  one  part  of  the  surface  slight  ridges  will  appear 
at  the  edges,  and  if  these  are  not  turned  out  the  lenses  will  chip 
the  least  bit,  perhaps  not  enough  so  they  cannot  be  taken  out  in 
beveling.  A  workman,  in  handling  quantities  of  lenses,  is  very 
apt  to  overlook  some  of  these  and,  when  located  in  the  finished 
job,  the  lenses  must  be  taken  out  of  the  mountings  and  the  chips 
run  out.  Occasionally  a  chip  on  the  top  or  bottom  of  the  lens 
can  be  taken  out  without  removing  the  lenses  from  the  mounting. 
but  care  must  be  used  not  to  strike  the  metal  on  the  stone.  A 
long,  quick  sweep  of  the  lens  is  required ;  do  not  attempt  a  short 
one,  as  this  will  give  the  lens  an  irregular  appearance.  Make  it 
as  long  as  possible  and,  of  course,  not  very  deep. 

If  one  has  plenty  of  time  the  surface  can  be  examined  at  this 
point  for  scratches,  but  as  it  necessitates  cleaning  the  lens  thor- 
oughly the  inspector  usually  waits  until  the  mounting  has  been 
trued  up.  He  can  then  wipe  the  lenses  once  and  give  the  job  the 
finishing  touches.  If  he  cleans  the  lenses  at  this  point  he  will  then 
soil  them  in  the  truing,  and  this  makes  an  extra  operation.  This 
may  seem  trifling  to  many  opticians,  but  every  move  counts  when 
examining  several  hundred  jobs  in  a  large  shop.  If  the  truing  has 
been  done  and  a  scratch  found,  a  new  lens  will  be  required.    You 


i8o  The  Making  of  a  Mechanical  Optician 

may  say  that  the  truing  must  be  done  again ;  that  is  true,  but  the 
inspector  takes  this  chance. 

One  may  make  the  suggestion  that  all  this  may  take  consider- 
able time  and  that  the  prescription  house  does  not  give  them 
this  attention.  This  is  not  so.  as  every  job  passes  through  this 
same  rigid  examination,  but  the  operation  to  a  trained  eye  re- 
quires a  very  few  seconds.  Practice  will  enable  any  optician  to 
be  very  critical  and  many  are  expert  in  this  work.  The  larger 
majority,  however,  we  are  afraid  do  not  inspect  their  jobs  at  all, 
but  depend  entirely  on  the  prescription  houses.  Although  the 
best  houses  rarely  make  a  mistake,  it  is  by  all  means  wrong  to 
place  a  pair  of  glasses  on  a  patient  without  giving  them  the 
proper  inspection. 

The  lenses  having  been  found  to  be  correct,  attention  is  then 
directed  to  the  frame  or  mounting.  If  it  is  a  rimless  spectacle 
we  first  note  the  drilling  to  .see  that  the  holes  are  on  a  line  and 
also  that  they  are  the  correct  distance  from  the  edge.  Should 
one  or  mcjre  of  the  holes  be  drilled  a  little  above  or  below  the 


Fig.  193 

line  the  strap  will  necessarily  be  fitted  at  an  angle.  It  also  gives 
the  lens  the  appearance  of  being  out  of  shape.  If  it  has  been 
drilled  "off"  but  slightly  the  strap  can  be  removed  and  the  hole 
filed  a  little  up  or  down,  as  the  case  may  be  (Fig.  193).  This  will 
naturally  enlarge  the  hole  to  some  extent,  but  the  strap  will  re- 
main fairly  tight. 

This  remedy  is  resorted  to  in  cases  of  emergency  only.  The 
most  satisfactory  way  is  to  fit  a  new  lens,  and  this  is  usually  done 
in  the  large  shops.  If  it  is  found  that  the  hole  has  been  drilled 
too  near  the  edge  the  strap  can  be  bent  down  slightly  with  a  pair 
of  No.  35  strap  pliers.     The  correct  method  is  to  make  a  slight 


The  Making  of  a  Mechanical  Optician  i8i 

kink  near  the  post  (Fig.  194)  and  under  no  circumstances  should 
the  points  be  bent  down,  leaving  an  opening  between  the  lens  and 
the  strap  (Fig.  195).  This  operation  is  explained  fully  m 
Chapter  IX  under  the  heading  ":\Iounting." 


Fig.  194 


At  this  point  should  also  be  noticed  whether  the  strap  has 
been  fitted  properly  to  the  surface  of  the  lens,  as  illustrated  in 
the  same  article.     If  the  strap  has  been  bent  to  a  wedge  shape  it 


will  be  possible  to  grasp  each  lens  and  twist  the  lens  in  the  strap 
considerably.  This  not  only  throws  the  glasses  out  of  alignment, 
but  is  very  liable  to  cause  the  lenses  to  chip  near  the  straps,  as 
the  lens-bearing  parts  slip  back  and  forth  on  the  edge.     If  the 


1 82  The  Making  of  a  Mechanical  Optician 

straps  are  not  correctly  fitted  in  this  respect  they  can  easily  be 
removed  and  fitted  with  the  strap  pliers.  It  is  unnecessary  to 
fit  new  lenses  as  the  holes  are  not  changed  materially  in  this 
operation.  When  inspecting  the  drilling  it  is  unnecessary  to 
have  the  spectacles  in  perfect  alignment,  although  it  is  perhaps 
easier  to  detect  any  variation  in  drilling.  With  practice  one  soon 
learns  to  judge  each  lens  separately  and  even  though  the  mount- 
ing may  be  all  out  of  shape,  it  is  a  simple  matter  to  tell  if  the 
straps  are  fitted  correctly. 

The  next  point  is  to  inspect  the  frame  or  mounting  and  see 
if  the  material  ordered  has  been  used.  Is  it  steel,  gold  or  filled? 
In  other  words,  is  it  what  the  prescription  calls  for?  Mistakes 
are  easily  made  in  numbers,  and  you  may  find  that  gold-filled  has 
been  supplied  when  gold  is  called  for,  or  vice  versa.  The  diflter- 
ence  in  the  metal  can  be  distinguished  by  the  trade-marks,  but  a 
trained  eye  will  readily  detect  the  difference  by  the  appearance 
and  style  of  the  mounting.  The  temples,  if  a  spectacle,  should 
be  measured  for  length;  also  as  to  whether  regular  or  cable 
temples  are  wanted.  Mistakes  of  this  character  are  very  frequent, 
and  with"  so  much  detail  to  remember,  it  is  a  simple  point  to  over- 
look. 

If  the  prescription  calls  for  eyeglasses  it  is  more  complicated, 
as  the  style  and  length  of  spring,  the  style  of  guards  and  the 
length  of  studs  must  be  noted.  With  fingerpiece  mountings  this 
is  simplified,  as  the  style  and  number  only  requires  attention. 
The  size,  being  designated  by  the  number,  we  soon  learn  to  judge 
the  correct  mounting.  The  inspection  of  the  mountings  or  frames 
from  the  optometrist's  standpoint  is  about  all  that  is  required 
of  an  inspector.  Frequently  a  pair  of  glasses  will  be  returned 
with  some  trifling  error  in  the  guards,  or  something  of  that  nature, 
and  a  letter  calling  attention  to  the  inspector's  carelessness.  While 
it  is  true  that  mistakes  of  any  kind  should  never  occur,  one  would 
never  refer  to  the  carelessness  of  an  inspector  if  he  realized  the 
detail  in  the  inspection  of  a  pair  of  glasses. 

After  inspecting  the  lenses  and  mountings  and  everything 
having  been  found  to  be  correct,  the  glasses  must  now  be  put  in 
condition  to  deliver  or  mail,  as  the  case  may  be.  The  first  opera- 
tion will  be  to  "line-up"  the  mounting ;  in  other  words,  bring 
the  straps  into  position,  so  that  when  the  spectacle  is  held  endwise 


The  Making  of  a  Mechanical  Optician 


183 


the  heads  of  the  screws  will  form  a  straight  line.  Then  hold 
the  spectacle  so  that  you  can  look  down  on  the  edge  and  see  if 
the  lenses  are  straight  in  this  respect  (Fig.  196).  If  they  are 
not,  they  will  have  to  be  brought  into  line  by  bending  one  shank 
up  or  down,  as  the  case  may  be.  For  this  operation  the  shank 
is  held  with  a  pair  of  flat  pliers,  either  snipe  nose,  flat  or  parallel 


Fig.  196 

jaw.  The  No.  40  plier,  which  is  used  for  adjusting  fingerpiece 
mountings  and  for  holding  endpieces,  on  account  of  the  narrow 
parallel  jaw,  is  very  convenient  for  this  work  also.  The  top 
of  the  bridge  is  grasped  with  the  thumb  and  forefinger  of  the 
left  hand  and  the  shank  of  the  bridge  with  the  pliers  in  the  right 
hand  (Fig.  197).  The  bridge  can  then  be  thrown  up  or  down  with 
the  left  hand  and  the  pliers  in  the  right  hand  held  stationary,  or 
the  bridge  held  securely  with  the  left  hand  and  tlie  shank  bent 


Fig.  197 

with  the  pliers  in  the  right.  If  judgment  is  used  before  chang- 
ing the  bridge,  it  is  a  very  easy  matter  to  learn  which  way  to 
throw  it,  but  to  the  inexperienced  it  may  be  found  that  although 
the  spectacles  have  been  straightened,  the  dimensions  will  not 
be  correct.  In  this  operation  it  will  be  seen  that  we  either  make 
the  bridge  higher  and  with  more  inset,  or  lower  and  more  outset. 
As  we  have  just  been  working  on  the  shanks  of  the  bridge, 
it  is  just  as  well  to  inspect  the  height  first.  If  it  is  too  high  or 
too  low,  bend  it  by  the  method  just  described,  bending  both  shanks, 


1 84 


The  Makimj  of  a  Mechanical  Optician 


of  course,  the  same  amount.  Next  turn  the  glasses  endwise  and 
inspect  tlie  inset  or  outset.  If  the  mounting  has  been  properly 
selected  and  bent  to  measurements  by  the  bender,  the  raising  and 
lowering  of  the  bridge  to  correct  height  should  also  place  the 
crest  in  the  proper  position  as  to  the  inset  or  outset.  If  these  are 
not  found  to  be  correct  it  must  be  changed  at  this  point. 


^^ 


Fig.  198 

At  this  time  it  is  well  to  measure  the  iiupillary  distance  and 
also  the  base  of  bridge,  as  if  we  find  it  necessary  to  change  one 
measurement  a  variation  at  some  other  point  may  be  of  assistance 
in  some  way.  For  example,  if  the  pupillary  distance  is  too  great 
and  the  base  of  the  bridge  is  also  wide,  it  will,  perhaps,  be  only 


Fig.  199 

necessary  to  bend  the  crest  of  the  bridge,  so  as  to  make  the  base 
narrower,  and  this  will  also  change  the  pupillary  distance  the 
required  amount.  If  the  base  is  too  narrow  the  operation  will  be 
vice  versa.     By  this  it  will  be  seen  that  in  the  inspection  of  a 


The  Makituj  of  a  Mechanical  Optician  185 

prescription  the  bridge  having  been  bent  to  the  required  dimen- 
sions before  mounting,  the  work  calls  for  slight  changes  only. 
Each  variation  is  so  slight  that  one  helps  the  other,  provided, 
however,  that  the  bridge  has  been  properly  selected  and  bent 
correctly.     When  selecting  a  bridge  for  a  prescription  and  bend- 


i 


Fig.  200 


ing  it  to  measurements,  it  requires  more  skill,  whereas  the  slight 
changes  that  are  necessary  in  inspecting  can  be  accomplished 
easily  by  anyone  having  had  a  little  practice. 

The  bridge,  having  been  straightened  and  bent  to  dimensions, 
we  turn  our  attention  to  the  endpieces  and  temples.  First,  see 
that  the  temples  set  back  the  right  amount ;  also  that  they  are 
even,  and  one  not  set  back  more  than  the  other.  The  prescription 
will  probably  give  the  distance  between  the  temples ;  this  distance 
is  measured  one  inch  from  the  endpieces.     Some  opticians  make 


Fig.  201 

the  mistake  by  measuring  a  frame  between  the  temples  at  the  end- 
pieces,  but  this  is  not  correct.  The  distance  at  the  endpieces  can 
be  four  inches  and  at  a  point  one  inch  from  the  endpieces  it  can 
be  45^  inches  (Fig.  198). 

Temples  can  be  set  back  almost  any  amount,  except  that  in 
extreme  cases,  for  verv  full  faces,  it  is  necessarv  to  use  extension 


i86  The  Making  of  a  Mrcliaiiical  Optician 

temples,  or  long  endpieces.  There  is  a  question,  perhaps,  which 
looks  the  best,  but  although  the  long  endpieces  (Fig.  199)  may 
look  the  best  off  the  face,  the  extension  temples  (Fig.  200)  are 
very  much  neater  on  the  face.  The  long  endpieces  extend  out 
so  far  that  they  are  very  conspicuous,  whereas  the  extension 
curving  around  the  temples  of  the  patient,  look  very  neat. 

Extension  temples  can  be  obtained  from  the  prescription 
houses,  or  they  can  be  bent  very  easily  with  pliers.  Always  select 
a  length  one-half  inch  longer  than  required,  as  the  bend  will  take 
up  about  that  amount  of  stock.  In  setting  back  the  temples  the 
tips  can  be  filed  in  steel  and  gold,  but  in  gold-filled  it  is  better  to 
use  a  pair  of  No.  42  endpiece  pliers  to  hold  the  joint  (Fig.  201). 
The  joint  is  held  by  the  plier  in  the  right  hand  and  the  temple 


Fig.  202 

grasped  with  the  thumb  and  forefinger  of  the  left,  as  close  to  the 
joint  as  possible.  The  temple  is  then  bent  backward  to  the  de- 
sired amount  arid,  if  held  as  described,  the  bend  cannot  be  noticed. 
Do  not  bend  them  as  ilkistrated  in  Fig.  202,  as  they  look  badly. 

The  temples  should  then  be  trued  with  thumb  and  forefinger 
so  that  there  will  be  no  kinks  in  them ;  also  that  the  straight 
part  is  perfectly  straight  and  a  natural  curve  to  the  tips.  See  that 
the  temples  curl  the  same  way  and  as  you  hold  the  spectacle 
squarely  in  front  of  you  with  the  temples  curling  toward  you, 
each  will  be  straight  and  not  bent  differently.  If  they  are  bent 
in  this  manner  they  do  not  fit  the  ears  and  also  do  not  look  well 
when  the  temples  are  closed.  If  the  prescription  calls  for  angular 
temples  bend  the  endpieces,  holding  them  with  the  Xo.  40  plier 
and  with  a  snipe-nose  plier  tilt  the  joint  the  required  amount. 
The  temples  are  also  brought  into  alignment  in  the  same  manner 
(Fig.  203).  Do  not  bend  the  temples  with  hollow  chop  pliers  so 
that  they  are  all  out  of  shape  (Fig.  204).     It  should  be  noticed 


The  Making  of  a  Mechanical  Optician  187 

if  the  temples  fit  well  in  the  joints ;  if  too  loose  they  fall  down, 
and  this  gives  a  very  poor  appearance  to  the  job. 

In  frameless  this  can  be  regulated  by  the  screw  in  the  end- 
piece,   but    in    frames   the   endpieces   must   be   brought   together 


Fig.  203 

better,  and  this  is  accomplished  by  removing  the  screw  and  the 
lens  if  desired,  but  this  is  unnecessary,  as  it  can  be  held  in  the 
frame  with  one  hand.  With  a  pair  of  snipe-nose  pliers  m  the 
right  hand  one  endpiece  is  grasped  and  bent  slightly  towards 
the  other.    The  screw  is  then  replaced,  and  as  the  endpieces  are 


dv.yfc 


Fig.  204 

brought  together  they  bind  on  the  outer  end,  so  that  the  temple 
is  held  tightly. 

When  screwing  the  endpieces  together  be  very  careful  that 
the  dowel  does  not  bind  before  it  slips  into  the  hole,  as  this  will 
cause  the  endpieces  to  spread  again.  It  is  carelessness  on  the 
part  of  the  grinder,  when  inserting  the  lenses  in  the  frame,  in 
allowing  the  dowel  to  strike  against  the  opposite  endpiece,  thereby 
spreading  them.     This  can  be  done  either  when  pulling  the  end- 


i88  The  Making  of  a  Mechanical  0[>ticiati 

pieces  together  with  phers,  or  when  inserting  the  screw.     Gold- 
filled,  especially,  will  not  stand  abuse  in  this  manner. 

The  inspection  is  now  complete  and  the  lenses  should  be 
cleaned.  In  many  places  the  inspectors  simply  breathe  on  the 
lenses  and  wipe  them  with  a  rag.  This  is  not  only  unsanitary, 
but  it  does  not  clean  the  lenses  properly.  An  atomizer  containing 
water  or  some  antiseptic  mixture  is  much  better,  as  the  spray 
cleans  around  the  straps  and  also  leaves  a  polish  on  the  lenses. 
A  rubber  atomizer  is  very  convenient,  as  it  can  lie  in  any  position 
on  the  table.  Glass  towels  are  the  best  for  wiping  lenses  and  if 
a  clean  one  is  used  each  day  there  will  be  no  danger  of  scratch- 
ing. The  axis  can  then  be  dotted  if  they  are  to  be  sent  out  in  this 
wav. 


The  Refractive  and 

Motor  Mechanism 

of  the  Eye 

By  WILLIAM  NORWOOD  SOUTER,  M.D. 

Associate  Ophthalmologist.  Episcopal  Eye,  Ear 
and  Throat  Hospital,  Washington,  D.  C. 

THIS  work  by  one  of  the  most  eminent  ophthal- 
mologists in  the  United  States,  brings  the 
science  of  eye  refraction  right  up  to  date  and 
embodies,  in  addition  to  the  profound  knowledge  of 
the  author,  all  the  researches  on  the  subject  that  experi- 
ence has  established  as  authoritative. 

The  geometric  and  mathematical  optics  on  which 
the  principles  of  optometry  are  based,  necessary  iitfor- 
iiiation  to  optical  students  of  to-day,  will  be  foimd  in 
simplified  form  in  the  Appendix  of  this  treatise. 

Students,  teachers  and  practitioners  alike,  in  study- 
ing this  book  or  using  it  for  reference,  have  the  assur- 
ance of  absolute  reliability  of  statement  and  complete 
elimination  of  the  misleading  fallacies  which  mar  the 
worth  of  many  works  on  this  subject. 

It  contains  350  pages  with  148  illustrations,  many 
entirely  original,  and  is  probably  the  only  scientific 
work  ever  published  in  which  every  single  reference 
was  verified  absolutely  by  the  author  himself. 

Sent  postpaid  to  any  part  of  the  world  on  receipt  of  price 

$2.00  (8s.  4d.) 

A* 

Published  by 
THE    KEYSTONE  PUBLISHINO  COMPANY 

809-811-813  NORTH   19th  STREET 
PHILADELPHIA,  LI,  S.  A. 


Physiologic  Optics 

Ocular  Dioptrics  —  Functions  of  tlie 

Retina  —  Ocular  Movements  and 

Binocular  Vision 

By   DR.   M.   TSCHERNING 

Director  of   the    Laboratory  of   Ophthalmology 
at  the  Sorbonne,  Paris 

A* 

AUTHORIZED   TRANSLATION 

By  CARL  WEILAND,  M.D. 

Former  Chief  of  Clinic  in  the  Eye  Department  of  the 
Jefferson  College  Hospital,  Philadelphia,  Pa. 

THIS  book  is  recognized  in  the  scientific  and  medical 
world  as  the  one  complete  and  authoritative  treatise 
on  physiologic  optics.  Its  distinguished  author  is 
admittedly  the  greatest  authority  on  this  subject, 
and  his  book  embodies  not  only  his  own  researches,  but  those 
of  the  several  hundred  investigators  who,  in  the  past  hundred 
years,  made  the  eye  their  specialty  and  life  study. 

Tscherning  has  sifted  the  gold  of  all  optical  research 
from  the  dross,  and  his  book,  as  now  published  in  English, 
with  many  additions,  is  the  most  valuable  mine  of  reliable 
optical  knowledge  within  reach  of  ophthalmologists.  It  con- 
tains 380  pages  and  212  illustrations,  and  its  reference  list 
comprises  the  entire  galaxy  of  scientists  who  have  made 
the  century  famous  in  the  world  of  optics. 

The  chapters  on  Ophthalmometry,  Ophthalmoscopy, 
Accommodation,  Astigmatism,  Aberration  and  Entoptic 
Phenomena,  etc. — in  fact,  the  entire  book  contains  so  much 
that  is  new,  practical  and  necessary,  that  no  refractionist  can 
afford  to  be  without  it. 

Bound  in  Cloth.  380  Pages,  212  Illustrations. 

Sent  postpaid  to  any  part  of  the  world  on  receipt  of  price 

$2.50  (10s.  5d.) 

Published  by 

THE  KEYSTONE   PUBLISHING   COMPANY 

809-811-813  NORTH  19th  STREET. 
PHILADELPHIA,  U.  S.  ,\. 


Tests  and  Studies 

of  the  Ocular 

Muscles 


By  ERNEST  E.  MADDOX,  M.D.,  F.R.C.S.,  Ed. 

Ophthalmic  Surgeon  to  the  Royal  Victoria  Hospital.  Bournemouth,  England  ; 
formerly  Syme  Surgical  Fellow.  Edinburgh  University 

THIS  book  is  universally  recognized  as  the 
standard  treatise  on  the  muscles  of  the  eye, 
their  functions,  anomalies,  insufficiencies,  tests 
and  optical  treatment. 
All  opticians  recognize  that  the  subdivision  of  refractive 
work  that  is  most  troublesome  is  muscular  anomalies. 
Even  those  who  have  mastered  all  the  other  intricacies 
of  visual  correction  will  often  find  their  skill  frustrated 
and  their  efforts  nullified  if  they  have  not  thoroughly 
mastered  the  ocular  muscles. 

The  eye  specialist  can  thoroughly  equip  himself 
in  this  fundamental  essential  by  studying  the  work  of 
Dr.  Maddox,  who  is  known  in  the  world  of  medicine 
as  the  greatest  investigator  and  authority  on  the  sub- 
ject of  eye  mascles. 

The  present  volume  is  the  second  edition  of  the 
work,  specially  revised  and  enlarged  by  the  author.  It 
is  copiously  illustrated  and  the  comprehensive  index 
greatly  facilitates  reference. 

Bound   in   Silk   Cloth  —  261  Pages  —  110  Illustrations. 
Sent  postpaid  to  any  part  of  the  world  on  receipt  of  price 

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The 

Principles  of  Refraction 

in  the  Human  Eye,  Based  on  the 
Laws  of  Conjugate  Foci 

By  SWAN  M.  BURNETT,  M.D.,  PH.D. 

Formerly  Professor  of  Ophthalmology  and  Otology  in  the  Georgetown 
University  Medical  School;   Director  of  the  Eye  and  Ear  Clinic, 
Central  Dispensary  and  Emergency  Hospital:  Ophthalmo- 
logist to  the  Children's  Hospital   and  to  Providence 
Hospital,  etc.,  Washington,  D.  C. 


X  this  treatise  the  student  is  given  a  condensed  but 
thorough  grounding  in  the  principles  of  refractioH 
according  to  a  method  which  is  both  easy  and  funda- 


I  mental.  The  few  laws  governing  the  conjugate  foci 
lie  at  the  basis  of  whatever  pertains  to  the  relations  of 
the  object  and  its  image. 

To  bring  all  the  phenomena  manifest  in  the  refraction  of 
the  human  eye  consecutively  under  a  common  explanation  by 
these  simple  laws  is,  we  believe,  here  undertaken  for  the  first 
time.  The  comprehension  of  much  which  has  hitherto  seemed 
diiificult  to  the  average  student  has  thus  been  rendered  much 
easier.  This  is  especially  true  of  the  theory  of  Skiascopy, 
which  is  here  elucidated  in  a  manner  much  more  simple  and 
direct  than  by  any  method  hitherto  offered. 

The  authorship  is  sufficient  assurance  of  the  thorough- 
ness of  the  work.  Dr.  Burnett  was  recognized  as  one  of  the 
greatest  authorities  on  eye  refraction,  and  this  treatise  may 
be  described  as  the  crystallization  of  his  life-work  in  this  field. 

The  text  is  elucidated  by  24  original  diagrams,  which 
were  executed  by  Chas.  F.  Prentice,  M.E.,  whose  pre-emi- 
nence in  mathematical  optics  is  recognized  by  all  ophthalmol- 
ogists. 

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ophthalmic  Lenses 

Dioptric  Formulae  for  Combined  Cylindrical 

Lenses,  The  Prism-Dioptry  and 

Other  Original  Papers 

By  CHARLES  F.  PRENTICE,  ME. 

A  new  and  revised  edition  of  all  the  original  papers  of  this  noted  author, 
combined  in  one  volume.  In  this  revised  form,  with  the  addition  of  recent 
research,  these  standard  papers  are  of  increased  value.  Combined  in  one 
volume,  thev  are  the  greatest  compilation  on  the  subject  of  lenses  extant. 
This  book  of  over  200  pages  contains  the  following  papers: 

Ophthalmic  Lenses.  j  ^    ,•    j  •     i  i    „„.= 

Dioptric  Formula  for  Cotnbined  Cylindrical  Lenses. 
The  Prism-Dioptry. 
A  Metric  System  of  Numbering  and  Measiirins;  Prisms. 

Tlie  KelHUun  ul  Ih.-  I'iisn,-ln..|.try  to  Ihe  .M.-t.-r  .Angle. 

Tlic  Kehuion  of  Ihe  Prism-lMoi.lry  to  the  Lens-Dioplry. 
The  Perfected  Prismometer. 

The  Prismometric  Scale.  „    .    ,    ,     •     r.  •   .■ 

On  the  Practical  Execution  of  Ophthalmic  Prescriptions 

involving;  Prisms.  c    i      j  k  .  .t.^ 

A  Problem  in  Cemented  Bi-Focal  Lenses.  Solved  b>  the 

Why  Strong  Cotiuii-Generic  Lenses  of  Equal  power  Fail 

'  to  Neutralize  Each  Other. 
The  Advantages  of  the  Sphero-Tonc  Lens. 
The  Iris,  as  Diaphragm  and  Photostat. 

Thl  Coi^Scti^n^of  Depleted  Dynamic  Refraction  (Presbyopia). 

PRESS  NOTICES  OF  THE  ORIGINAL  EDITION: 

OPHTHALMIC  LENSES 

"  The  work  stands  alone,  in   its  present  form,  a  compendium  of  the  various  laws  of 

nhvsics  relative  to  this  subject  that  are  so  ditficult  of  access  ii  scattered  treanses 

I    -  —yew  Eiifjland  Medical  Gazeltf. 

"  It  is  the  most  complete  and  best  illustrated  book  on  this  special  subject  ever  published." 
'  —UoroltiijUal  Reticle,  I<ii:if  iuik. 

"Of  all  the  simple  treatises  on  the  properties  of  lenses  that  we  have  seen,  this  is  incom- 
parablv  the  best.  ...  The  teacher  of  the  average  medical  student  will  hail  this 
little  work  as  a  great  boon."         -Ari-liiics  of  V/Mliiilinolog!/,  cdiM  hij  Jl.  Kiiiip,,,  M.l>. 

Bound  in  Silk  Cloth.  HO  Original  Diagrams. 

Sent  postpaid  to  any  part  of  the  world  on  receipt  of  price 

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PHILADELPHIA,  V.  S  .\. 


The  Optician's  Manual 

Volume  I. 

By  C.  H.  BROWN,  M.  D. 

Graduate  University  of    Pennsylvania:    Professor    of    Principles  and 

Practice  of  Optometry;  formerly  Physician  to  the  Philadelphia 

Hospital;    Author  of  "Clinics  in  Optometry,"  etc. 

THE  OPTICIAN'S  MANUAL,  Vol.  I.  was  the  most 
popular  and  useful  work  on  practical  refraction 
ever  written,  and  has  been  the  entire  optical  edu- 
cation of  many  hundred  successful  ref ractionists. 
The  knowledge  it  contains  was  more  effective  in  building  up 
the  profession  of  optometry  than  any  other  educational 
factor.  It  is,  in  fact,  the  foundation  structure  of  all  op- 
tometric  knowledge  as  the  titles  of  its  ten  chapters  show : 

Chapter  I.— Introductory  Remarks. 
Chapter  II.— The  Eye  Anatomically. 
Chapter     III.— The  Eye  Optically;  or. 

The  Physiology  of  Vision. 

Chapter    IV Optics. 

Chapter      V. — Lenses. 

Chapter    VI. — Numbering  of  Lenses. 

Chapter  VII.    The  Use  and  Value  of  Glasses. 

Chapter  VIII.— Outfit  Required. 

Chapter     IX. — Method  of  Examination. 

Chapter      X. — Presbyopia. 

In  its  present  revised  and  enlarged  form  this  volume  is 
the  recognized  standard  text-book  on  practical  refraction, 
being  used  as  such  in  all  schools  of  Optics.  A  study  of  it 
is  essential  to  an  intelligent  appreciation  of  its  companion 
treatise,  The  Optician's  Manual,  \^ol.  II.  A  comprehensive 
index  adds  much  to  its  usefulness  to  both  student  and 
practitioner. 

Bound  in  cloth— 422  pages— colored  plates  and  illustrations. 
Sent  postpaid  to  any  part  of  the  world  on  receipt  of  price 

$1.50  (6s.  3d.) 


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The  Optician's  Manual 

VOL.  II. 

By  C.  H.  BROWN,  M.D. 

Graduate  University  of  Pennsylvania  :  Professor  of  Optics  and  Refraction  ; 

Formerly  Physician  in  Philadelphia  Hospital :  Author  of  "CHnics  in 

Optometry  ";  *'  State  Board  Questions  and  Ans'wers  ";  Etc. 

THE  Optician's  Manual,  Vol.  II.,  is  a  direct 
continuation  of  The  Optician's  Manual,  Vol.  I., 
being  a  much  more  advanced  and  compre- 
hensive treatise.  It  covers  in  minutest  detail 
the  four  great  subdivisions  of  practical  eye  refraction,  viz  : 

MYOPIA 

HYPERMETROPIA 
ASTIGMATISM 
MUSCULAR  ANOMALIES 

It  contains  the  most  authoritative  and  complete 
researches  up  to  date  on  these  subjects,  treated  b)-  the 
master  hand  of  an  eminent  oculist  and  optical  teacher. 
It  is  thoroughly  practical,  explicit  in  statement  and 
accurate  as  to  fact.  All  refractive  errors  and  complica- 
tions are  clearly  explained,  and  the  methods  of  correc- 
tion thoroughly  elucidated. 

This  book  fills  the  last  great  want  in  higher  refrac- 
tive optics,  and  the  knowledge  contained  in  it  marks 
the  standard  of  professionalism. 

Bound  in  Cloth.  408  pages,  with  illustrations. 

Sent  postpaid  to  any  part  of  the  world  on  receipt  of  price 

$1.50  (6s.  3d.) 


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Clinics  in  Optometry 

By  C.  H.  BROWN,  M.  D. 

Cruduate  University  of  Pennsylvania:  Professor  of  Principles  and 

Practice  of  Optometry  :  formerly  Physician  to  the 

Philadelphia  Hospital ;   Author  of  the 

Optician's  Manual,  Etc. 


CLINICS  IN  OPTOMETRY"  is  a  unique 
work  in  the  field  of  practical  refraction  and 
fills  a  want  that  has  been  seriously  felt  both 
by  oculists  and  optometrists. 
The  book  is  a  compilation  ot  optometric  clinics,  each 
clinic  being  complete  in  itself  Together  they  cover 
all  manner  of  refractive  eye  defects,  from  the  simplest 
to  the  most  complicated,  giving  in  minutest  detail  the 
proper  procedure  to  follow  in  the  diagnosis,  treatment 
and  correction  of  all  such  defects. 

Practically  every  case  that  can  come  before  you 
is  thoroughly  explained  in  all  its  phases  in  this  useful 
volume,  making  mistakes  or  oversights  impossible  and 
assuring  correct  and  successful  treatment. 

The  author's  experience  in  teaching  the  science  of 
refraction  to  thousands  of  pupils  peculiarly  equipped 
him  for  compiling  these  clinics,  all  of  which  are  actual 
cases  of  refractive  error  that  came  before  him  in  his 
practice  as  an  oculist. 

A  copious  index  makes  reference  to  any  particular 
case,  test  or  method,  the  work  of  a  moment. 

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State  Board  Examinations 

QUESTIONS  and  ANSWERS 

By  C.  H.  BROWN,  M.  D. 

I  University  of  Pennsylvania  781 

Formerly  Physician  Philadelphia  Hospital;  Professor  Principles 

and  Practice  of  Optometry  ;  Author  The  Optician's  Manual, 

Volumes  I  and  II;  Clinics  in  Optometry;  etc.,  etc. 

THIS  volume  was  specially  compiled  for  the 
tjuidance  and  instruction  of  candidates  for 
examination  before  optometry  boards  and  for 
optical  students  generally.  It  contains  five  hundred 
questions  with  answers,  the  questions  being  carefully 
selected  from  the  examination  papers  set  by  the  State 
Boards  of  Examiners  in  Optometry. 

The  book  was  compiled  to  meet  the  needs  of  those 
who  ma\'  find  it  compulsory  or  advisable  to  take  a  State 
Board  examination,  and  for  optical  students  generally. 

The  questions  are  probably  more  fully  answered 
than  a  State  examining  board  would  expect,  the  idea 
being  to  give  complete  information  on  the  special  sub- 
ject brought  out  by  each  question. 

The  contents  are  classified  under  different  headings, 
which  gives  the  work  the  character  of  a  text-book  and 
facilitates  study  and  reference. 

As  the  questions  were  selected  with  a  view  to 
avoiding  repetition,  the  book  will  be  found  to  cover 
thoroughly  every  paper  set  by  any  of  the  State 
Examining  Boards. 

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Record-Book  of 
Optometric 
Examinations 

A  RECORD-BOOK,  wherein  to  record  opto- 
/  ^  metric  examinations,  is  an  indispensable  ad- 
/       ^  junct  to  an  optometrist's  outfit. 

The  Keystone  Record-Book  of  Optometric  Exami- 
nations was  specially  prepared  for  this  purpose.  It 
excels  all  others  in  being  not  only  a  record-book,  but 
an  invaluable  guide  in  examination. 

The  book  contains  two  hundred  record  forms  with 
printed  headings,  suggesting,  in  the  proper  order,  the 
course  of  examination  that  should  be  pursued  to  obtain 
most  accurate  results. 

Each  book  has  an  index,  which  enables  the  optom- 
etrist to  refer  instantly  to  the  case  of  any  particular 
patient. 

The  Keystone  Record-Book  diminishes  the  time 
and  labor  required  for  examinations,  obviates  possible 
oversights  from  carelessness,  and  assures  a  systematic 
and  thorough  examination  of  the  eye,  as  well  as 
furnishes  a  permanent  record  of  all  examinations. 

Sent  postpaid  to  any  part  of  the  world  on  receipt  of  price 

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